OM Combining Crazyhouse and Force of the Fallen crashes battle

[Giga-Chandélure]

What type of bug are you reporting? OM

What is the bug?
The battle crashes in Broken Cup with Mayhem, Revelationmons, FOTF, Protean Palace and Crazyhouse rules, when a Pokémon faints for some reason, but I don't really understand why and what are the causing rules
https://replay.pokemonshowdown.com/gen9brokencup-2226387363
https://replay.pokemonshowdown.com/gen9brokencup-2226387098
https://replay.pokemonshowdown.com/gen9brokencup-2226387258
https://replay.pokemonshowdown.com/gen9brokencup-2226380514
https://replay.pokemonshowdown.com/gen9brokencup-2226387347
https://replay.pokemonshowdown.com/gen9brokencup-2226398008
https://replay.pokemonshowdown.com/gen9brokencup-2226403771

Are you able to replicate it? If so, how?
/chall brokencup@@@mayhem,!camomonsmod,revelationmonsmod,forceofthefallenmod,crazyhouserule,!inversemod,proteanpalacemod
the bug may appear in a few turns

 

[Chains of Markov]

This bug occurs whenever a stolen mon (through crazyhouse) faints and tries to pass on its move (as in forceofthefallen). So the second time any mon dies the game will crash. This is not specific to Broken Cup or any of the other mods in the replays.

Force of the Fallen requires some bookkeeping in the code, such as keeping track of what the "true" last move is as moves are being added. Presumably that does not get passed on properly when a pokemon is captured, thus the bug. I have no idea how to fix it myself, but maybe it'd be fine to simply disallow this combination of mods instead.