It is not known to evolve into or from any other Pokémon.
Along with Raikou and Entei, it is one of the Legendary beasts resurrected by Ho-Oh after the burning of the Brass Tower. Of the three Legendary beasts, Suicune is said to represent the rains that quenched the flames of the burning Brass Tower.
Suicune is a slim, quadrupedal, blue, mammalian Pokémon with white, diamond-shaped markings. Its face and underside are white as well. Suicune has a thick, purple mane that resembles the aurora borealis and two white, streamer-like tails that wave forward. It has a long, white snout. Suicune has a large, hexagonal, cerulean blue crest on its forehead with two prongs on either side of the base. It has red eyes, a small tuft of fur under its chin, and small paws with white paw pads.
Suicune has the power to walk across water and purify dirty water with one touch. It travels across grasslands in search of water to purify by following the north wind. Northern winds always seem to blow stronger in its presence. In Pokémon Crystal, Suicune is said to be the closest of the Legendary beasts to Ho-Oh. It is also said to have a link to the Unown. In the anime, Suicune is heroic, serious, and calm during dangerous situations. Suicune is believed to be both the embodiment of the north winds and compassion of pure spring waters.
Suicune made its debut in Don't Touch That 'dile, where Ash and his friends first encountered one as they were heading towards New Bark Town. Suicune was seen standing on a small island in a lake, appearing as a mysterious silhouette of blue energy. At first, Ash did not understand what Pokémon it was and wanted to catch it. However, Suicune leaped into the fog and vanished as soon as Ash made an attempt to battle it.
Eusine wanted to catch Suicune and sent out his Alakazam to battle it. Alakazam used Disable, but Suicune easily blocked it with a Mirror Coat. It then used Roar to send Alakazam back into its Poké Ball and fled from the area before Eusine could even react. The brief encounter led Eusine to pursue Suicune, in the hopes of seeing it again one day.
In Healing the Healer!, Ash and Goh encountered a Suicune that was being targeted by a group of Pokémon hunters. Goh caught Suicune in order to save and heal it. In the end, even though the hunters were arrested and Goh attempted to release Suicune, it chose to remain under his ownership.
Suicune reappears again in Super Smash Bros. Ultimate, functioning the same as in previous games. In this game, it can also be summoned from a Master Ball.
Melee trophy information
This mystical aurora Pokémon constantly journeys in search of places with pure flowing water. Suicune wields the power to instantly purify any contaminated water it finds. Some say Suicune is the north wind reborn. Its strange and dramatic story is told over the course of the Crystal version of the Pokémon game.
Brawl trophy information
"An Aurora Pokémon. It has the power to instantly purify even the filthiest water. Suicune is said to be the reincarnation of the northern wind, so when it shows up, so does that wind. Suicune uses the move Aurora Beam--aurora light focused into a powerful beam. Along with inflicting damage, this attack also lowers the target's attack power."
3DS/Wii U trophy information
Suicune trophy in Super Smash Bros. for 3DS
NA: A Legendary Pokémon that emerged from the ashes of the Burned Tower, Suicune is a Water-type Pokémon easily identified by its long, purple mane. In battle, it'll head toward a nearby fighter and fire an Aurora Beam all the way to the edge of the screen. If you get hit, you'll be frozen solid!
PAL: Suicune is one of the Legendary Pokémon from the Burned Tower in Ecruteak City. Its mane is said to resemble an aurora floating over it. If summoned in battle, it'll make its way straight for a nearby fighter and unleash its Aurora Beam. The target, frozen in place, is unable to resist as it's blown off the stage.
When asked if Suicune was based on any particular animal, Muneo Saitō described its creation process to come together easily and fell into a motif that felt "leopard-like". This motif may have been a homage from Fūjin, the Shinto god of the wind, who wears leopard skin. Its mane also looks similar to aurora. Its build, crest, and ability to walk on water bear similarities to the Qilin.
Water-type Suicune corresponds to the rain that put out the Brass Tower according to its legend, at the same time Raikou represents the lightning that striked it and Entei represents the fire that burned it.
Suicune may be a combination of 水 sui (water), 水晶 suishō (crystal), and 君 kun (monarch).