A_Fire
From ZDoom Wiki
A_Fire
A_Fire (int height)
Places the calling actor directly in front of its target, with a z offset of height. This only works for missiles with the SEEKERMISSILE flag.
Examples
The Arch-Vile from Doom uses this function in its fire attack's Decorate code to keep the fire placed on its target:
actor ArchvileFire { Game Doom SpawnID 98 RenderStyle Add Alpha 1 +NOBLOCKMAP +NOGRAVITY States { Spawn: FIRE A 2 bright A_StartFire FIRE BAB 2 bright A_Fire FIRE C 2 bright A_FireCrackle FIRE BCBCDCDCDEDED 2 bright A_Fire FIRE E 2 bright A_FireCrackle FIRE FEFEFGHGHGH 2 bright A_Fire Stop } }