UB can play off the same strong commons and uncommons as UR does, and it has some great expensive spells to pair them with like Sephiroth's Intervention, Ice Magic, Dreams of Laguna (flashback), and Sidequest: Hunt the Mark
Instead of collecting the four crystals, Ill gather these four precons for a review of Final Fantasy Commander
Stuck in Summoners Sanctum (decent) Stuck in Summoner's Sanctum is a fairly-costed answer to big vanilla creatures and some artifacts, though it doesnt remove abilities like Tamiyo's Compleation did
You also need to do this if its returned to hand with a bounce effect like Unsummon, or if it moves to any other zone at all from the battlefield
None of these abilities is necessarily preposterous on their own, but each gives a different option - and in formats such as Modern and Legacy (the latter of which this card is banned in) they build up into an insurmountable advantage
The most likely of those decks seems to be Vengevine or maybe even Dredge and Endurance gives green players some much-appreciated protection from those strategies