From Creatures Wikia
_P1_ and _P2_ are CAOS commands used in message passing.
_P1_ and _P2_ are the names of two local variables in agent scripts. Sometimes, the engine needs to pass data to a script which are not accessible from one of the usual commands (FROM and so on) which usually contain message information. In this case the engine uses the parameters _P1_ and _P2_. For instance, script 73 (Raw Key Down) is sent the keycode in _P1_.
Parameters can also be sent to scripts using MESG WRT+.
_P1_ and _P2_ can be modified within scripts. This has no more effect on the outside of the script than does modifying VAxx variables.
- Script numbers contain details of parameters passed