My mod I'm currently working on.

[WALP]

Instead of trying to fit both the player and the monster into the same callback, maybe just add a seperate callback for the monster that calls the same function?

This is the HPL3 version of AddEntityCollideCallback from HPL2:

Entity_AddCollideCallback(const tString &in asParentName,const tString &in asChildName,const tString &in asFunction)