A_Burst
From ZDoom Wiki
A_Burst (string classname)
Spawns a random numbers of actors of type classname, positions them all around the calling actor, and then destroys the calling actor, removing it instantly from the game. The amount spawned is relative to the calling actor's size, so a very large actor will spawn many more classnames than a much smaller actor. An actor with radius 20 and height 64 spawns, on average, around 40 things.
Examples
This would make a modified grenade that would split in its death state into an actor called "MiniGrenade"
Actor ClusterBomb : Grenade { States { Death: MISL B 8 Bright A_Burst "MiniGrenade" MISL C 6 Bright MISL D 4 Bright Stop } }