I didn't know where else to do so, so here I go. I'd like to report a bug on Showdown where the terrains are not working properly. A couple of days ago, on psychic terrain a Mimikyu was able to use Shadow Sneak (a move with priority), but I didn't save the replay at the time. Now, on Misty terrain, a Rotom was able to use Will-o-wisp (a status move) and fortunately I did save the replay this time.
Replay - See turn 1
Replay - See turn 1