A_FaceTarget is an action that immediately changes the actor's angle to be facing its target. If the actor doesn't have a target however, this action will do nothing. In SRB2, this is frequently used by a number of Objects and other actions.
Code – A_FaceTarget
// Function: A_FaceTarget
// Description: Immediately turn to face towards your target.
// var1 = unused
// var2 = unused
void A_FaceTarget(mobj_t *actor)
if (LUA_CallAction("A_FaceTarget", actor))
actor->angle = R_PointToAngle2(actor->x, actor->y, actor->target->x, actor->target->y);