### Function: SetSeeInvis(Spawn, Enable)

**Description:** Toggles an NPC’s ability to see invisible on or off.

**Parameters:**

`Spawn`: Spawn – The NPC whose invis detection to set.
`Enable`: Boolean – true to grant see-invis; false to revoke it.

**Returns:** None.

**Example:**

```lua
-- Example usage (temporarily allow a boss to see invis during a phase)
SetSeeInvis(BossNPC, true)
```