diff --git a/internal/monsters/monsters.go b/internal/monsters/monsters.go
index c0cd7e8..eba2b5c 100644
--- a/internal/monsters/monsters.go
+++ b/internal/monsters/monsters.go
@@ -3,8 +3,6 @@ package monsters
 import (
 	"dk/internal/store"
 	"fmt"
-	"sort"
-	"sync"
 )
 
 // Monster represents a monster in the game
@@ -21,14 +19,11 @@ type Monster struct {
 }
 
 func (m *Monster) Save() error {
-	monsterStore := GetStore()
-	monsterStore.UpdateMonster(m)
-	return nil
+	return GetStore().UpdateWithRebuild(m.ID, m)
 }
 
 func (m *Monster) Delete() error {
-	monsterStore := GetStore()
-	monsterStore.RemoveMonster(m.ID)
+	GetStore().RemoveWithRebuild(m.ID)
 	return nil
 }
 
@@ -36,13 +31,13 @@ func (m *Monster) Delete() error {
 func New() *Monster {
 	return &Monster{
 		Name:    "",
-		MaxHP:   10,         // Default HP
-		MaxDmg:  5,          // Default damage
-		Armor:   0,          // Default armor
-		Level:   1,          // Default level
-		MaxExp:  10,         // Default exp reward
-		MaxGold: 5,          // Default gold reward
-		Immune:  ImmuneNone, // No immunity by default
+		MaxHP:   10,
+		MaxDmg:  5,
+		Armor:   0,
+		Level:   1,
+		MaxExp:  10,
+		MaxGold: 5,
+		Immune:  ImmuneNone,
 	}
 }
 
@@ -63,279 +58,122 @@ func (m *Monster) Validate() error {
 	return nil
 }
 
-// Immunity constants for monster immunity types
+// Immunity constants
 const (
 	ImmuneNone  = 0
-	ImmuneHurt  = 1 // Immune to Hurt spells
-	ImmuneSleep = 2 // Immune to Sleep spells
+	ImmuneHurt  = 1
+	ImmuneSleep = 2
 )
 
-// MonsterStore provides in-memory storage with O(1) lookups and monster-specific indices
+// MonsterStore with enhanced BaseStore
 type MonsterStore struct {
-	*store.BaseStore[Monster]               // Embedded generic store
-	byLevel                   map[int][]int // Level -> []ID
-	byImmunity                map[int][]int // Immunity -> []ID
-	allByLevel                []int         // All IDs sorted by level, then ID
-	mu                        sync.RWMutex  // Protects indices
+	*store.BaseStore[Monster]
 }
 
-// Global in-memory store
-var monsterStore *MonsterStore
-var storeOnce sync.Once
+// Global store with singleton pattern
+var GetStore = store.NewSingleton(func() *MonsterStore {
+	ms := &MonsterStore{BaseStore: store.NewBaseStore[Monster]()}
 
-// Initialize the in-memory store
-func initStore() {
-	monsterStore = &MonsterStore{
-		BaseStore:  store.NewBaseStore[Monster](),
-		byLevel:    make(map[int][]int),
-		byImmunity: make(map[int][]int),
-		allByLevel: make([]int, 0),
-	}
+	// Register indices
+	ms.RegisterIndex("byLevel", store.BuildIntGroupIndex(func(m *Monster) int {
+		return m.Level
+	}))
+
+	ms.RegisterIndex("byImmunity", store.BuildIntGroupIndex(func(m *Monster) int {
+		return m.Immune
+	}))
+
+	ms.RegisterIndex("allByLevel", store.BuildSortedListIndex(func(a, b *Monster) bool {
+		if a.Level == b.Level {
+			return a.ID < b.ID
+		}
+		return a.Level < b.Level
+	}))
+
+	return ms
+})
+
+// Enhanced CRUD operations
+func (ms *MonsterStore) AddMonster(monster *Monster) error {
+	return ms.AddWithRebuild(monster.ID, monster)
 }
 
-// GetStore returns the global monster store
-func GetStore() *MonsterStore {
-	storeOnce.Do(initStore)
-	return monsterStore
-}
-
-// AddMonster adds a monster to the in-memory store and updates all indices
-func (ms *MonsterStore) AddMonster(monster *Monster) {
-	ms.mu.Lock()
-	defer ms.mu.Unlock()
-
-	// Validate monster
-	if err := monster.Validate(); err != nil {
-		return
-	}
-
-	// Add to base store
-	ms.Add(monster.ID, monster)
-
-	// Rebuild indices
-	ms.rebuildIndicesUnsafe()
-}
-
-// RemoveMonster removes a monster from the store and updates indices
 func (ms *MonsterStore) RemoveMonster(id int) {
-	ms.mu.Lock()
-	defer ms.mu.Unlock()
-
-	// Remove from base store
-	ms.Remove(id)
-
-	// Rebuild indices
-	ms.rebuildIndicesUnsafe()
+	ms.RemoveWithRebuild(id)
 }
 
-// UpdateMonster updates a monster efficiently
-func (ms *MonsterStore) UpdateMonster(monster *Monster) {
-	ms.mu.Lock()
-	defer ms.mu.Unlock()
-
-	// Validate monster
-	if err := monster.Validate(); err != nil {
-		return
-	}
-
-	// Update base store
-	ms.Add(monster.ID, monster)
-
-	// Rebuild indices
-	ms.rebuildIndicesUnsafe()
+func (ms *MonsterStore) UpdateMonster(monster *Monster) error {
+	return ms.UpdateWithRebuild(monster.ID, monster)
 }
 
-// LoadData loads monster data from JSON file, or starts with empty store
+// Data persistence
 func LoadData(dataPath string) error {
 	ms := GetStore()
-
-	// Load from base store, which handles JSON loading
-	if err := ms.BaseStore.LoadData(dataPath); err != nil {
-		return err
-	}
-
-	// Rebuild indices from loaded data
-	ms.rebuildIndices()
-	return nil
+	return ms.BaseStore.LoadData(dataPath)
 }
 
-// SaveData saves monster data to JSON file
 func SaveData(dataPath string) error {
 	ms := GetStore()
 	return ms.BaseStore.SaveData(dataPath)
 }
 
-// rebuildIndicesUnsafe rebuilds all indices from base store data (caller must hold lock)
-func (ms *MonsterStore) rebuildIndicesUnsafe() {
-	// Clear indices
-	ms.byLevel = make(map[int][]int)
-	ms.byImmunity = make(map[int][]int)
-	ms.allByLevel = make([]int, 0)
-
-	// Collect all monsters and build indices
-	allMonsters := ms.GetAll()
-
-	// Build level and immunity indices
-	for id, monster := range allMonsters {
-		ms.byLevel[monster.Level] = append(ms.byLevel[monster.Level], id)
-		ms.byImmunity[monster.Immune] = append(ms.byImmunity[monster.Immune], id)
-		ms.allByLevel = append(ms.allByLevel, id)
-	}
-
-	// Sort allByLevel by level first, then by ID
-	sort.Slice(ms.allByLevel, func(i, j int) bool {
-		monsterI, _ := ms.GetByID(ms.allByLevel[i])
-		monsterJ, _ := ms.GetByID(ms.allByLevel[j])
-		if monsterI.Level == monsterJ.Level {
-			return ms.allByLevel[i] < ms.allByLevel[j]
-		}
-		return monsterI.Level < monsterJ.Level
-	})
-
-	// Sort level indices by ID
-	for level := range ms.byLevel {
-		sort.Ints(ms.byLevel[level])
-	}
-
-	// Sort immunity indices by level, then ID
-	for immunity := range ms.byImmunity {
-		sort.Slice(ms.byImmunity[immunity], func(i, j int) bool {
-			monsterI, _ := ms.GetByID(ms.byImmunity[immunity][i])
-			monsterJ, _ := ms.GetByID(ms.byImmunity[immunity][j])
-			if monsterI.Level == monsterJ.Level {
-				return ms.byImmunity[immunity][i] < ms.byImmunity[immunity][j]
-			}
-			return monsterI.Level < monsterJ.Level
-		})
-	}
-}
-
-// rebuildIndices rebuilds all monster-specific indices from base store data
-func (ms *MonsterStore) rebuildIndices() {
-	ms.mu.Lock()
-	defer ms.mu.Unlock()
-	ms.rebuildIndicesUnsafe()
-}
-
-// Retrieves a monster by ID - O(1) lookup
+// Query functions using enhanced store
 func Find(id int) (*Monster, error) {
 	ms := GetStore()
-	monster, exists := ms.GetByID(id)
+	monster, exists := ms.Find(id)
 	if !exists {
 		return nil, fmt.Errorf("monster with ID %d not found", id)
 	}
 	return monster, nil
 }
 
-// Retrieves all monsters - O(1) lookup (returns pre-sorted slice)
 func All() ([]*Monster, error) {
 	ms := GetStore()
-	ms.mu.RLock()
-	defer ms.mu.RUnlock()
-
-	result := make([]*Monster, 0, len(ms.allByLevel))
-	for _, id := range ms.allByLevel {
-		if monster, exists := ms.GetByID(id); exists {
-			result = append(result, monster)
-		}
-	}
-	return result, nil
+	return ms.AllSorted("allByLevel"), nil
 }
 
-// Retrieves monsters by level - O(1) lookup
 func ByLevel(level int) ([]*Monster, error) {
 	ms := GetStore()
-	ms.mu.RLock()
-	defer ms.mu.RUnlock()
-
-	ids, exists := ms.byLevel[level]
-	if !exists {
-		return []*Monster{}, nil
-	}
-
-	result := make([]*Monster, 0, len(ids))
-	for _, id := range ids {
-		if monster, exists := ms.GetByID(id); exists {
-			result = append(result, monster)
-		}
-	}
-	return result, nil
+	return ms.GroupByIndex("byLevel", level), nil
 }
 
-// Retrieves monsters within a level range (inclusive) - O(k) where k is result size
 func ByLevelRange(minLevel, maxLevel int) ([]*Monster, error) {
 	ms := GetStore()
-	ms.mu.RLock()
-	defer ms.mu.RUnlock()
-
 	var result []*Monster
 	for level := minLevel; level <= maxLevel; level++ {
-		if ids, exists := ms.byLevel[level]; exists {
-			for _, id := range ids {
-				if monster, exists := ms.GetByID(id); exists {
-					result = append(result, monster)
-				}
-			}
-		}
+		monsters := ms.GroupByIndex("byLevel", level)
+		result = append(result, monsters...)
 	}
 	return result, nil
 }
 
-// Retrieves monsters by immunity type - O(1) lookup
 func ByImmunity(immunityType int) ([]*Monster, error) {
 	ms := GetStore()
-	ms.mu.RLock()
-	defer ms.mu.RUnlock()
-
-	ids, exists := ms.byImmunity[immunityType]
-	if !exists {
-		return []*Monster{}, nil
-	}
-
-	result := make([]*Monster, 0, len(ids))
-	for _, id := range ids {
-		if monster, exists := ms.GetByID(id); exists {
-			result = append(result, monster)
-		}
-	}
-	return result, nil
+	return ms.GroupByIndex("byImmunity", immunityType), nil
 }
 
-// Saves a new monster to the in-memory store and sets the ID
+// Insert with ID assignment
 func (m *Monster) Insert() error {
 	ms := GetStore()
-
-	// Validate before insertion
-	if err := m.Validate(); err != nil {
-		return fmt.Errorf("validation failed: %w", err)
-	}
-
-	// Assign new ID if not set
 	if m.ID == 0 {
 		m.ID = ms.GetNextID()
 	}
-
-	// Add to store
-	ms.AddMonster(m)
-	return nil
+	return ms.AddMonster(m)
 }
 
-// Returns true if the monster is immune to Hurt spells
+// Helper methods
 func (m *Monster) IsHurtImmune() bool {
 	return m.Immune == ImmuneHurt
 }
 
-// Returns true if the monster is immune to Sleep spells
 func (m *Monster) IsSleepImmune() bool {
 	return m.Immune == ImmuneSleep
 }
 
-// Returns true if the monster has any immunity
 func (m *Monster) HasImmunity() bool {
 	return m.Immune != ImmuneNone
 }
 
-// Returns the string representation of the monster's immunity
 func (m *Monster) ImmunityName() string {
 	switch m.Immune {
 	case ImmuneNone:
@@ -349,17 +187,13 @@ func (m *Monster) ImmunityName() string {
 	}
 }
 
-// Calculates a simple difficulty rating based on stats
 func (m *Monster) DifficultyRating() float64 {
-	// Simple formula: (HP + Damage + Armor) / Level
-	// Higher values indicate tougher monsters relative to their level
 	if m.Level == 0 {
 		return 0
 	}
 	return float64(m.MaxHP+m.MaxDmg+m.Armor) / float64(m.Level)
 }
 
-// Returns the experience reward per hit point (efficiency metric)
 func (m *Monster) ExpPerHP() float64 {
 	if m.MaxHP == 0 {
 		return 0
@@ -367,7 +201,6 @@ func (m *Monster) ExpPerHP() float64 {
 	return float64(m.MaxExp) / float64(m.MaxHP)
 }
 
-// Returns the gold reward per hit point (efficiency metric)
 func (m *Monster) GoldPerHP() float64 {
 	if m.MaxHP == 0 {
 		return 0
diff --git a/internal/store/store.go b/internal/store/store.go
index 1120a0a..9f8247b 100644
--- a/internal/store/store.go
+++ b/internal/store/store.go
@@ -6,35 +6,329 @@ import (
 	"os"
 	"path/filepath"
 	"reflect"
+	"sort"
+	"strings"
 	"sync"
 )
 
-// Store provides generic storage operations
-type Store[T any] interface {
-	LoadFromJSON(filename string) error
-	SaveToJSON(filename string) error
-	LoadData(dataPath string) error
-	SaveData(dataPath string) error
+// Validatable interface for entities that can validate themselves
+type Validatable interface {
+	Validate() error
 }
 
-// BaseStore provides generic JSON persistence
+// IndexBuilder function type for building custom indices
+type IndexBuilder[T any] func(allItems map[int]*T) any
+
+// BaseStore provides generic storage with index management
 type BaseStore[T any] struct {
-	items    map[int]*T
-	maxID    int
-	mu       sync.RWMutex
-	itemType reflect.Type
+	items         map[int]*T
+	maxID         int
+	mu            sync.RWMutex
+	itemType      reflect.Type
+	indices       map[string]any
+	indexBuilders map[string]IndexBuilder[T]
 }
 
 // NewBaseStore creates a new base store for type T
 func NewBaseStore[T any]() *BaseStore[T] {
 	var zero T
 	return &BaseStore[T]{
-		items:    make(map[int]*T),
-		maxID:    0,
-		itemType: reflect.TypeOf(zero),
+		items:         make(map[int]*T),
+		maxID:         0,
+		itemType:      reflect.TypeOf(zero),
+		indices:       make(map[string]any),
+		indexBuilders: make(map[string]IndexBuilder[T]),
 	}
 }
 
+// Index Management
+
+// RegisterIndex registers an index builder function
+func (bs *BaseStore[T]) RegisterIndex(name string, builder IndexBuilder[T]) {
+	bs.mu.Lock()
+	defer bs.mu.Unlock()
+	bs.indexBuilders[name] = builder
+}
+
+// GetIndex retrieves a named index
+func (bs *BaseStore[T]) GetIndex(name string) (any, bool) {
+	bs.mu.RLock()
+	defer bs.mu.RUnlock()
+	index, exists := bs.indices[name]
+	return index, exists
+}
+
+// RebuildIndices rebuilds all registered indices
+func (bs *BaseStore[T]) RebuildIndices() {
+	bs.mu.Lock()
+	defer bs.mu.Unlock()
+	bs.rebuildIndicesUnsafe()
+}
+
+func (bs *BaseStore[T]) rebuildIndicesUnsafe() {
+	allItems := make(map[int]*T, len(bs.items))
+	for k, v := range bs.items {
+		allItems[k] = v
+	}
+
+	for name, builder := range bs.indexBuilders {
+		bs.indices[name] = builder(allItems)
+	}
+}
+
+// Enhanced CRUD Operations
+
+// AddWithRebuild adds item with validation and index rebuild
+func (bs *BaseStore[T]) AddWithRebuild(id int, item *T) error {
+	bs.mu.Lock()
+	defer bs.mu.Unlock()
+
+	if validatable, ok := any(item).(Validatable); ok {
+		if err := validatable.Validate(); err != nil {
+			return err
+		}
+	}
+
+	bs.items[id] = item
+	if id > bs.maxID {
+		bs.maxID = id
+	}
+
+	bs.rebuildIndicesUnsafe()
+	return nil
+}
+
+// RemoveWithRebuild removes item and rebuilds indices
+func (bs *BaseStore[T]) RemoveWithRebuild(id int) {
+	bs.mu.Lock()
+	defer bs.mu.Unlock()
+	delete(bs.items, id)
+	bs.rebuildIndicesUnsafe()
+}
+
+// UpdateWithRebuild updates item with validation and index rebuild
+func (bs *BaseStore[T]) UpdateWithRebuild(id int, item *T) error {
+	return bs.AddWithRebuild(id, item)
+}
+
+// Common Query Methods
+
+// Find retrieves an item by ID
+func (bs *BaseStore[T]) Find(id int) (*T, bool) {
+	bs.mu.RLock()
+	defer bs.mu.RUnlock()
+	item, exists := bs.items[id]
+	return item, exists
+}
+
+// AllSorted returns all items using named sorted index
+func (bs *BaseStore[T]) AllSorted(indexName string) []*T {
+	bs.mu.RLock()
+	defer bs.mu.RUnlock()
+
+	if index, exists := bs.indices[indexName]; exists {
+		if sortedIDs, ok := index.([]int); ok {
+			result := make([]*T, 0, len(sortedIDs))
+			for _, id := range sortedIDs {
+				if item, exists := bs.items[id]; exists {
+					result = append(result, item)
+				}
+			}
+			return result
+		}
+	}
+
+	// Fallback: return all items by ID order
+	ids := make([]int, 0, len(bs.items))
+	for id := range bs.items {
+		ids = append(ids, id)
+	}
+	sort.Ints(ids)
+
+	result := make([]*T, 0, len(ids))
+	for _, id := range ids {
+		result = append(result, bs.items[id])
+	}
+	return result
+}
+
+// LookupByIndex finds single item using string lookup index
+func (bs *BaseStore[T]) LookupByIndex(indexName, key string) (*T, bool) {
+	bs.mu.RLock()
+	defer bs.mu.RUnlock()
+
+	if index, exists := bs.indices[indexName]; exists {
+		if lookupMap, ok := index.(map[string]int); ok {
+			if id, found := lookupMap[key]; found {
+				if item, exists := bs.items[id]; exists {
+					return item, true
+				}
+			}
+		}
+	}
+	return nil, false
+}
+
+// GroupByIndex returns items grouped by key
+func (bs *BaseStore[T]) GroupByIndex(indexName string, key any) []*T {
+	bs.mu.RLock()
+	defer bs.mu.RUnlock()
+
+	if index, exists := bs.indices[indexName]; exists {
+		switch groupMap := index.(type) {
+		case map[int][]int:
+			if intKey, ok := key.(int); ok {
+				if ids, found := groupMap[intKey]; found {
+					result := make([]*T, 0, len(ids))
+					for _, id := range ids {
+						if item, exists := bs.items[id]; exists {
+							result = append(result, item)
+						}
+					}
+					return result
+				}
+			}
+		case map[string][]int:
+			if strKey, ok := key.(string); ok {
+				if ids, found := groupMap[strKey]; found {
+					result := make([]*T, 0, len(ids))
+					for _, id := range ids {
+						if item, exists := bs.items[id]; exists {
+							result = append(result, item)
+						}
+					}
+					return result
+				}
+			}
+		}
+	}
+	return []*T{}
+}
+
+// FilterByIndex returns items matching filter criteria
+func (bs *BaseStore[T]) FilterByIndex(indexName string, filterFunc func(*T) bool) []*T {
+	bs.mu.RLock()
+	defer bs.mu.RUnlock()
+
+	var sourceIDs []int
+
+	if index, exists := bs.indices[indexName]; exists {
+		if sortedIDs, ok := index.([]int); ok {
+			sourceIDs = sortedIDs
+		}
+	}
+
+	if sourceIDs == nil {
+		for id := range bs.items {
+			sourceIDs = append(sourceIDs, id)
+		}
+		sort.Ints(sourceIDs)
+	}
+
+	var result []*T
+	for _, id := range sourceIDs {
+		if item, exists := bs.items[id]; exists && filterFunc(item) {
+			result = append(result, item)
+		}
+	}
+	return result
+}
+
+// Common Index Builders
+
+// BuildStringLookupIndex creates string-to-ID mapping
+func BuildStringLookupIndex[T any](keyFunc func(*T) string) IndexBuilder[T] {
+	return func(allItems map[int]*T) any {
+		index := make(map[string]int)
+		for id, item := range allItems {
+			key := keyFunc(item)
+			index[key] = id
+		}
+		return index
+	}
+}
+
+// BuildCaseInsensitiveLookupIndex creates lowercase string-to-ID mapping
+func BuildCaseInsensitiveLookupIndex[T any](keyFunc func(*T) string) IndexBuilder[T] {
+	return func(allItems map[int]*T) any {
+		index := make(map[string]int)
+		for id, item := range allItems {
+			key := strings.ToLower(keyFunc(item))
+			index[key] = id
+		}
+		return index
+	}
+}
+
+// BuildIntGroupIndex creates int-to-[]ID mapping
+func BuildIntGroupIndex[T any](keyFunc func(*T) int) IndexBuilder[T] {
+	return func(allItems map[int]*T) any {
+		index := make(map[int][]int)
+		for id, item := range allItems {
+			key := keyFunc(item)
+			index[key] = append(index[key], id)
+		}
+
+		// Sort each group by ID
+		for key := range index {
+			sort.Ints(index[key])
+		}
+
+		return index
+	}
+}
+
+// BuildStringGroupIndex creates string-to-[]ID mapping
+func BuildStringGroupIndex[T any](keyFunc func(*T) string) IndexBuilder[T] {
+	return func(allItems map[int]*T) any {
+		index := make(map[string][]int)
+		for id, item := range allItems {
+			key := keyFunc(item)
+			index[key] = append(index[key], id)
+		}
+
+		// Sort each group by ID
+		for key := range index {
+			sort.Ints(index[key])
+		}
+
+		return index
+	}
+}
+
+// BuildSortedListIndex creates sorted []ID list
+func BuildSortedListIndex[T any](sortFunc func(*T, *T) bool) IndexBuilder[T] {
+	return func(allItems map[int]*T) any {
+		ids := make([]int, 0, len(allItems))
+		for id := range allItems {
+			ids = append(ids, id)
+		}
+
+		sort.Slice(ids, func(i, j int) bool {
+			return sortFunc(allItems[ids[i]], allItems[ids[j]])
+		})
+
+		return ids
+	}
+}
+
+// Singleton Management Helper
+
+// NewSingleton creates singleton store pattern with sync.Once
+func NewSingleton[S any](initFunc func() *S) func() *S {
+	var store *S
+	var once sync.Once
+
+	return func() *S {
+		once.Do(func() {
+			store = initFunc()
+		})
+		return store
+	}
+}
+
+// Legacy Methods (backward compatibility)
+
 // GetNextID returns the next available ID atomically
 func (bs *BaseStore[T]) GetNextID() int {
 	bs.mu.Lock()
@@ -45,10 +339,7 @@ func (bs *BaseStore[T]) GetNextID() int {
 
 // GetByID retrieves an item by ID
 func (bs *BaseStore[T]) GetByID(id int) (*T, bool) {
-	bs.mu.RLock()
-	defer bs.mu.RUnlock()
-	item, exists := bs.items[id]
-	return item, exists
+	return bs.Find(id)
 }
 
 // Add adds an item to the store
@@ -85,8 +376,11 @@ func (bs *BaseStore[T]) Clear() {
 	defer bs.mu.Unlock()
 	bs.items = make(map[int]*T)
 	bs.maxID = 0
+	bs.rebuildIndicesUnsafe()
 }
 
+// JSON Persistence
+
 // LoadFromJSON loads items from JSON using reflection
 func (bs *BaseStore[T]) LoadFromJSON(filename string) error {
 	bs.mu.Lock()
@@ -148,7 +442,7 @@ func (bs *BaseStore[T]) SaveToJSON(filename string) error {
 		items = append(items, item)
 	}
 
-	data, err := json.MarshalIndent(items, "", "  ")
+	data, err := json.MarshalIndent(items, "", "\t")
 	if err != nil {
 		return fmt.Errorf("failed to marshal to JSON: %w", err)
 	}
@@ -178,6 +472,7 @@ func (bs *BaseStore[T]) LoadData(dataPath string) error {
 	}
 
 	fmt.Printf("Loaded %d items from JSON\n", len(bs.items))
+	bs.RebuildIndices() // Rebuild indices after loading
 	return nil
 }