Ok so it is time for my official Victini pre-reqs post...
First off, let's go over this thing's wide af movepool...
Physical: (STAB in
Italics)
V-Create, Bolt Strike, U-turn,
Zen Headbutt
Special: (STAB in
Italics)
Blue Flare, Energy Ball, Grass Knot, Focus Blast,
Psychic,
Psyshock, Thunder, Glaciate, Solar Beam,
Stored Power
Status: Sunny Day, Trick Room, Taunt, Thunder Wave, Trick, Will-O-Wisp
While it doesn't look to have a "ton" of moves, it has everything it needs. It has two solid ways to get around would-be checks and counters with Thunder / Bolt Strike hitting all bulky Waters not named Swampert, who gets bopped by Grass Knot. Even Rock-types, such as Rhyperior and Tyrantrum, are not going to like taking a Grass Knot or Glaciate respectively. It can effectively run a ton of sets such as Life Orb, Choice Band, Weakness Policy + Trick Room, and Choice Scarf (That is also the order in viability of its sets imo as well). While a lot has changed with things such as FatMence, Tyrantrum, and even Dragalge and the fact that it was banned pre-ORAS means this meta may have settled enough for Victini to be allowed back in UU. With metagame trends such as Pursuit Mega Aeroactyl and Krookodile, Victini may actually fare "better" in this meta so that it can stay around. Also a pretty cool calc...
0- Atk Mandibuzz Foul Play vs. 0 HP / 0 Def Victini: 260-308 (76.2 - 90.3%) -- guaranteed OHKO after Stealth Rock
Mandibuzz, a fairly new Pokemon, may be able to actually tank a V-Create if Physically Defensive or if given some defensive investment.
Next up, let's look at its typing...
Weaknesses: Dark, Ghost, Ground, Rock, Water
Resistances: Fairy, Fighting, Fire, Grass, Ice, Psychic, Steel
Now while Victini has a slew of common weaknesses (Ground, Rock, Water, Dark) it usually can tank a hit thanks to its across the board base 100 stats. Its true assets come with its resistances. Have a resist to Fairy, Fighting, Grass, and Psychic means it can tank a lot of hits from common walls / offensive mons and fire back a base 180 BP STAB move in V-Create.
Lastly, the power of Victini...
While base 100 stats across the board may seem underwhelming with things like Salamence, who has a base 130 Attack, or Azelf, who has a base 125 Special Attack, it makes up for it by having high BP moves with STAB V-Create, Thunder, Bolt Strike, and so on. Also with its movepool and its high power moves, it can effectively go mixed a lot better than say Azelf because it is also backed by amazing bulk even with a hindering nature.
As of right now, I am not too sure about Victini coming back but maybe that is just my insecurities of the last time it was here and there has been enough changes to maybe allow it to stay around this time.