EVENT_EGS is a Game Event.
This event is triggered when a new sprite is spawned on the map.
This event run for all actors, thus the gamevar THISACTOR refers to the ID of the sprite that is executing the code.
Internally, this is the moment the sprite structures and gamevars are reset for the sprite ID.
In comparison, EVENT_SPAWN runs for all sprites that pre-exist when the map is loaded and newly spawned sprites, and internally is used for changing the properties of specific sprites (such as enemies, etc).
Note that EVENT_EGS and EVENT_SPAWN are triggered the moment the sprite is spawned.
useractor notenemy ACTOR espawn PIGCOP setactor[RETURN].pal 1 enda onevent EVENT_EGS ifactor PIGCOP spritepal 2 endevent
In this case, the PIGCOP palette will be 1, because EVENT_EGS takes place before the lines below the espawn command.
Deleting sprites during EVENT_EGS may cause problems, since some hard-coded functions may try to change their properties after they were spawned (similar to the espawn example above).
EVENT_EGS can be used to save the original sprite owner before it's changed.