A very specialized form of A_Countdown.
It decreases by one the calling actor's special1 field. If this field becomes negative or null, the calling actor is jumps to its Death state. Otherwise, nothing else happens.
This codepointer is restricted to actors deriving from PoisonCloud because the special1 field might be used for different purposes by other classes or restricted codepointers.
See PoisonCloud for an example.