How to make a unit not spawn if item to spawn unit is used

[smaxcana]

I have a boss unit but i only want one be ingame at a time. How do I make it so it dosent spawn another from an item if theres 1 already ingame?
more info in image:

the ingame part of the image is without the limit

[kyle691]

Use the ‘number of units of unit type’ function to check if there is already a unit with the boss unit type in the game, before creating another boss unit. Here’s the entity script you could put on the item.