A_SetAngle
From ZDoom Wiki
A_SetAngle (float angle)
Sets the calling actor's angle to angle. It can be used with the angle DECORATE variable to modify the actor's current angle.
Examples
This zombie spins in circles in his spawn state.
actor SpinningZombieMan : ZombieMan replaces ZombieMan { States { Spawn: POSS ABCD 4 A_SetAngle(15 + angle) loop } }