Hey folks
This is easily my favorite Ultra Beast. It has the most balanced, usable, and arguably normal distribution compared to its fellows, with the lowest stat being a workable 61 speed. It's pretty much the only UB that can take a hit from either a physical or a special attack and recover effectively. Those defensive stats are a godsend, not to mention its remarkable typing. It even has offensive potential; a 107 SpAtt is nothing to sneeze at (which combined with those defensive stats brings to mind another OU staple *cough* *Rotom-W* *cough*), and it's blessed with a movepool that wouldn't look out of place on a fast special sweeper.
However, I personally didn't opt for special offense or defense when I used her in the early days of the new gen. It seems like an affront to Celesteela's design not to take advantage of its unrivaled weight combined with a 101 attack, that mind you can be boosted, and Heavy Slam. My physically offensive set, with Heavy Slam, Earthquake, Seed Bomb/Flame Charge, and Leech Seed, allowed me to win several battles with her alone, or simply as the core.
Admittedly an unexpected flamethrower or thunderbolt would put her out of commission, but the general ability of Celesteela to absorb hits (and health) made her a veritable tank with little defensive investment outside of HP. Additionally, with the correct teammates, those weaknesses can be mitigated somewhat. A Landorus-T, Celesteela, Rotom-W combo is a threat to behold.
So, yeah, I think Celesteela is definitely going to be an OU powerhouse, and whether the user wants to make her a hard-hitter or a hit-taker is up to them.
Oh by the way this is my first post so hi!