how do i make them die after they buy something

there are wisps in the begining of my map witch you use to buy your hero. how do i make it so the wisps die once they choose a hero?

oh and 1 more thing. how do i get those wight letters to appear when someone enters a region? i use to know how to do that but i forgot.

Event - A unit finished training a unit

Action - Remove unit training unit.

um i cant find the event that you told me to use.

i found the action but not the event

Unit - Generic Unit Event...

that didnt work is there any other way?

if you want i could give you my map and you could do it yourself cuz mabye i did somethign wrogn but i dont think so.

the whisps BUY the hero? why dont you make the heros training time to 1 (0 inpossible) and let the heros be trained than it would work with this trigger ...

but if the player may only have 1 hero you can also make this:
event: unit enters (playable map area)
conditons: boolean - (triggering unit) is a hero = true
actions: pick all unit owned by (owner of (triggering unit)) of type whisp and do: kill |remove| (picked unit)

ok thanks but i cant find the action can you please tell me were that one is.