Meet Victini, the Gen 5 member of the Mythical BST600 club, so as with all the members he is cute, legendary and as always has a Base Stat Total of 600 divided 6 ways across it's stats, making Victini pretty versatile and can run a variety of different options.
However Victini unlike his counterparts Mew, Celebi, Shaymin, Jirachi and Manaphy does not have a particularly kind typing and ability to allow for it to be so able to set up so well or avoid residual damage from status or hazards (Stealth Rocks of course) *side note: No Victini does not learn any stat raising moves like Mew, Manaphy or Celebi
But Victini is no amateur, what he lacks in longevity he makes up for in power, Victini has access to the most powerful base power move in the game (that doesn't require self sacrifice) V-Create, a base 180 Fire move to which he gets STAB for, that ,okay, do involve some stat drops but for that raw power you can forgive it.
Victini also has a unique ability we know as Victory Star
All Pokemon on your side of the field including Victini has each of its move accuracy increased by 10% (that is 10% of the move's original accuracy, not an added 10%)
This essentially means that Will O Wisp and Fire Blast have their accuracy upgraded to 93%, Zen Headbutt becomes 99% and Bolt Strike, Blue Flare and V-Create become 100%
And i'll just mention for the hell of it Focus Blast and Thunder become 77% accurate, as well all know Victini might as well be blindfolded because these always miss when you need them to hit the most... but I digress
In some formats Victini has access to some other powerful moves (which he stole from some prominent legendaries mind you)
Such as Blue Flare and Bolt Strike and even Glaciate (for coverage)
So Victini can do some real damage with these moves and that's his schtick.
However these powerful moves save for V-Create not being present in Gen 6 distributions of Victini are a harsh blow to him, severely hindering his coverage and raw power.
I like my Victinis not Mixed
Victini @ Choice Scarf/Choice Band/Life Orb
Nature: Adamant/Jolly
Ability: Victory Star
EVs: 252 Atk/252 Spe/4 Defense
-V-create/Flareblitz
-Bolt Strike/Wild Charge
-U-turn
-Zen Headbutt
So this is assuming you can use moves available in previous generations, I am inclined in listing this set because if Bolt Strike CAN be used it SHOULD be used, it is extremely valuable coverage.
U-Turn is for pivoting but as with any Fire type, Victini cannot pivot with Stealth Rocks.
Zen Headbutt is Victini's only physical Psychic attack, which takes advantage of his STAB and coverage
V-Create is not negotiable if it's available, it's Victini's most devastating attack, it OHKOs whatever it can that doesn't resist it or prepare for it, things that do resist it such as Hydreigon take nearly half their health too, if for whatever reason you cannot use V-Create use Flareblitz or just don't use Victini at all, V-Create is its trump card
Here is an idea of how strong V-Create can be
252+ Atk Adamant Victini with no Life Orb or Choice Band V-create vs. 252 HP / 252+ Def Cresselia: 90-106 (39.6 - 46.6%) -- guaranteed 3HKO with or without Leftovers recovery
252+ Atk Adamant Victini with no Life Orb or Choice Band V-create vs. 252 HP / 252+ Def Thick Fat Mega Venusaur: 90-108 (48.1 - 57.7%) -- 89.1% chance to 2HKO
That is power even if no one runs those sets on a Cresselia or Mega Venusaur it should give you an idea as to how strong Victini's V-Create can be against dedicated walls
Final slot goes to Bolt Strike for coverage against Flying types and Water Types such as Politoed, Suicune and Primal Kyogre
It can do at least 48% of damage to the HP of even the bulkiest Suicune, again the problem is Bolt Strike is not legal in Gen 6 native Victini, you will probably need to substitute this with Wildcharge but the drop in power is very noticeable and the recoil adds to Victini longevity
Victini is a wallbreaker and good revenge killer but it's also a Fire type so it can burn you like crazy but it's about as bulky as you'd expect from a bonfire, don't abuse V-Create either unless you can freely switch Victini or want to try out a TR gimmick, Victini's Defenses and Speed go down by one stage with each use, that would just make Victini as sturdy as a lit match.
V is for Victory!... depending on RNG
Victini @ Choice Scarf/Life Orb
Nature: Timid/Hasty/Naive
Ability: Victory Star
EVs: 252 SpA/252 Spe/4 Attack or 4 Defense or 4 SpD
-Fire Blast/Searing Shot/Blue Flare/V-Create
-Thunderbolt/Thunder
-Psyshock/Psychic
-Energy Ball/Focus Blast
This is another Victini sweeping set since Victini can't do much more than attacking, it learns no significant boosting moves or support moves.
But what it does have is an abundance of amazing Fire type attacks to look at
Fire Blast becomes somewhat reliable thanks to Victory Star and is a high powered move no with almost no drawback. Searing Shot is another option to play with, there is a drop in power and the PP is exactly the same however it offers a 30% chance to burn, so think of it as a slightly more powerful Scald that is Fire STAB for Victini. Blue Flare if available is the best option but again, not always legal in official Pokemon battle competitions online, V-Create is there if you want a slightly mixed Victini, it's power is too good to pass up so on Hasty or Naive sets it's an options
Thunderbolt is for coverage but if you are daring you can forgo that for Thunder, it's now 77% accurate but still is very unpredictable.
Psyshock or Psychic is there depending on the nature you are running and the inclusion of V-Create.
The last slot is very much up to gut feelings, Energy Ball is there for coverage against Pokemon like Swampert, Gastrodon, Rhyperior and such
There is the option of Focus Blast but like Thunder still very risky