Victini is a Pokeball Pokemon canidate for SSB4.
If Victini is released, he'll follow the player who released him, and utilize his Victory Star ability on him/her. That player will begin to emit a fiery red aura, which gives the strength of his/her physical, indirect, and magic attacks a 1.5x power boost. The effects of Victory Star remain in effect until Victini disappears, which typically happens after 10 seconds have passed.
If the player that Victini is helping has his/her current damage at 100%+, Victini will aid that player even further by utilizing Searing Shot to temporarily stun opponents within range. This in return will make it easier for the player to take advantage of Victory Star's power boost.