It is not known to evolve into or from any other Pokémon.
Victini and the macarons
Victini is a small, rabbit-like Pokémon with large, pointed ears which form the letter V. It has large, blue eyes and a round, cream head, which is comparatively large compared to its small, cream body, while the tops of its ears, crest, and extremities are all orange. Its bulbous arms and legs are rounded to make a sort of "cuff" before ending with small, three-fingered hands and two-toed feet. It has two pointed teeth that can be seen on its upper jaw. It also has two cream winglike tails, which allows it to fly. Though timid, it is a caring Pokémon; it will fight if its friends are in danger.
A Victini appeared in Pikachu, What's This Key?. It was one of the Mythical Pokémon visited by Pikachu and his friends, courtesy of Klefki's keys. It rescued Pikachu and brought him back to safety as he was falling into a chasm.
Victini appears as a Poké Ball Pokémon, after playing 100-Man Smash at least once. It uses Victory Star, which causes fighters (and teammates, if any) who send it out to gain immunity to knockback and have their attack power boosted.
NA: This Psychic/Fire-type Pokémon shares the limitless energy it creates with others. In Smash Bros., Victini uses Victory Star to power up the fighter that brought it into battle. The fighter won't flinch from damage and will launch foes easier, as well as glow with power. They aren't invincible, though...
PAL: Victini can create an endless supply of energy and share it with others. Its Victory Star move makes the other fighter who summoned it glow with power from head to toe. As long as they're glowing, their launch ability will shoot up and they'll never flinch. That said, they're not invincible - Victini isn't a miracle-worker.
Victini's appearance seems to be based on うさぎリンゴ usagi-ringo, a method of cutting apple slices to make them look similar to rabbits. Conceptually, it might draw inspiration from Nike, the Greek, winged goddess of victory, or Victoria, the Roman equivalent of Nike. Its tail wings may be a reference to Nike's wings.
Its theme of "V" could be linked to it being somewhat of the fifth Generation's mascot, "V" being the Roman numeral for 5. "V" could also derive from the initial for victory.
Victini may be a combination of victory and destiny, teeny, or tiny.
In other languages
From a combination of victory and destiny, teeny, or tiny.