A_Stop
From ZDoom Wiki
A_Stop
(no parameters)
This stops the actor's current movement by setting its acceleration and speed to 0. This can also be used on players, monsters and anything else that is moving vertically or horizontally.
Examples
ACTOR SoulStopper : LostSoul { States { Missile: SKUL C 10 bright A_FaceTarget SKUL D 4 bright A_SkullAttack SKUL CDCDCDC 4 Bright SKUL C 0 A_Stop Goto See } }
This Lost Soul flies through the air to attack but stops after a short distance. Without A_Stop it would return to its See state while still flying towards its target.