Welcome to Smogon! Take a moment to read the Introduction to Smogon for a run-down on everything Smogon, and make sure you take some time to read the global rules.
Feels like a lot of gate keeping with ou and ubers. We don't retest ubers because "what does it add to a metagame" having more options could lead to more players and more attention to the tier. Not so much saying darkrai is good or bad but I'm saying the mindset of refusing retests, especially...
I just think y'all underestimate it or play it too commonly to other walls. Its main function would be to spread toxic and heal, for example using icy wind on a sweeper switch and suddenly that switch in is both toxic and at -1 speed. It can uturn out a predicted bad matchup. It can sub up, or...
Honestly for BM ursaluna I could see it being fighting/ground with its signature move being a dark type move, considering we have shit like order up dodonzo and its a dragon move.
Not only that but stamina lets it spiral very quickly especially with possibly even better physical bulk when it evolves. So happy its on something besides mud horse