Used by the routines at MOVE_ARCS, MOVE_ACTOR, SPAWN_MONSTER, MOVE_BAT, MOVE_HOPPER, MOVE_FACE, COUNTDOWN_ACTOR, MOVE_GHOST, MOVE_WITCH and MOVE_FACING_FLYER.

Field +$0F of the actor record is a countdown. Almost every call is a no-op that just decrements it; only on the tick where it reaches zero does control go to SPIN_SPELL.