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
What are the main MTG Arena deck archetypes
Also, he's very strong at playing defense with his instant speed able Phasing out and if you can protect him, you can win fast in a multiplayer game, and the more in the game the better he is
That's why Upheaval is such a bomb: there are virtually no ways to deal with it, and once it is cast you can end up with two to three creatures plus a land on the board while your opponent literally has nothing, and has a hand full of sixteen cards they need to discard down to seven
Both will be available for purchase at local game stores and mass retail locations later this year