I had both Prankster and Mycelium Might active at the same time in Random Battle Mayhem, and Toxic did not work against the opponent when Comatose was active. I think that Prankster just completely overtook the effects of Mycelium Might, unless for some reason Mycelium Might does not go through Comatose the same way it does to Good as Gold and Purifying Salt.
The interaction happens on turn 17 in here:
https://replay.pokemonshowdown.com/gen9randombattlemayhem-1805590992
BUG STATUS: NOT A BUG, Mold breaker-like effects don't affect Comatose.
I would also like to mention that Contrary properly reverses the stat gains for all stat boosting abilities such as Speed Boost and Moxie, but it does not do the same for Zamazenta's Dauntless Shield and you still get the +1 defense boost on swap in. I don't have the replay of the game where that one happened though because it was a few days ago and I forgot to save it, but my opponent might have submitted it because they also mentioned in the chat that it was probably a bug.
BUG STATUS: NOT A BUG, Contrary affects only the user. If this happened in an OM, then that goes to the respective OM thread.