This question already has an answer here:
This question was inspired by an answer in this question. Suppose the Player Characters are attempting to protect their little village from a huge monster, Godzilla in this case. Obviously they'd get xp if they murdered Godzilla with their swords or banded together to sing a moving song to convince the enormous beast to seek a meal elsewhere.
However, would they get Xp for luring Mothra into Godzilla's path and having the two titans duke it out (thus preventing their village from being destroyed)?
The question that inspired this was specific for 5th edition, so I'd prefer answers from that ruleset, though if any of the older systems have an interesting take on it, I'm happy to read it.