Rocket Raccoon is a raccoon from the planet Halfworld that has received several enhancements, upping his intelligence and battle awareness. He protects the colony as a ranger, and currently explores the realm outside of Halfworld as an interplanetary explorer.
For more information, check his Marvel Universe wiki page
Rocket Raccoon is a very small and nimble trap and keepaway based character with a variety of special moves and mobility options to trick and frustrate his opponents. The range on his normals is incredibly short and rather limited, but he makes up for that with his amazing mobility using his float, Rocket Skates and Tunnel Rat special moves to move around the screen quickly.
Rocky's defensive tools in Ultimate Marvel vs. Capcom 3 range from a variety of proximity mine based traps including his Claymore, Angel Gift and Grab Bag special moves, his Mad Hopper hyper combo and projectile based attacks like Spitfire and Pendulum. These in combination with his Oil Bomb (ignited by using his standing :h: or Spitfire) and assists, he is able to control a considerable amount of space at any given time he is on screen.
That isn't to say that Rocket can't excel near the opponent, however, as his quick maneuverability can make him hard to block and a real nuisance up close with the aid of assists and Tunnel Rat. The flame carpet created by a detonated Oil Bomb can lock down the opponent for a while, leaving you time to mix up with Tunnel Rat, Rocket Skates and instant overheads using his float abilities.
Rocket's health tied with Akuma and Strider Hiryu as one of the lowest in the game at 750,000 HP. While his variety of weapons to control space and small hitbox make him difficult to hit, if he does he'll likely be finished off in a single combo. His damage output isn't terribly high and his combo potential is limited due to the awkwardness of his normals, so up close he'll have to rely on mixing up his opponent several times into order to kill.
Using Rocket effectively will involve using all of his traps and projectiles appropriately on the defensive and capitalizing on chances to open up the opponent when the chance arises to go on the offensive.
"Come on!" - Normal Attacks
:l: - Jab
:d::l: - Crouching jab
:m: - Short left hook
:d::m: - Low tail sweep
:h: - Laser pistol shot angled down. Ignites Oil Bomb
:d::h: - Crouching laser pistol shot angled upward. Ignites Oil Bomb
:f::h: - Rocket propelled dash where Rocky charges at the enemy with a knife in hand. Special cancellable
: - Launches the opponent with a swing of his tail
j.:l: - Jumping kick
j.:m: - A rocket propelled dashing headbutt in the air
j.:h: - Jumping knife slash
j.:s: - Tosses a grenade that explodes immediately next to him. It has a disjointed hitbox and does chip damage. Special cancellable
"Eat this!" - Special Attacks
:qcf::atk: [Air OK]
- Shoots a slow moving projectile. The angle is dependent on the button pressed. :l: angles downward, :m: goes straight forward, and :h: angles upward. It can be rapid fired twice with a second button press. OTG property. Ignites Oil Bomb
:qcb::l: - "Boulder trap!" Lays down a proximity mine that, when triggered, drops a boulder on the opponent. Hits overhead.
:qcb::m: - "Shrapnel trap!" Rocky lays down a proximity mine that explodes into shrapnel near the opponent.
:qcb::h: - "Net trap!" Lays down a proximity mine that, when triggered, captures the opponent in an electrified net and suspends them in mid-air.
:dp::l: - Tosses a balloon that spreads oil on the ground when it lands. :h: ignites the oil on the ground and creates a fire puddle that lasts for a short time. When hit in the air, Oil Bomb causes an explosion that OTGs.
:dp::m: - "Bear trap!" Rocket stomps the ground and sets off a spiked trap. OTG property.
:dp::h: - "Log trap!" Rocket ducks as a large log swings over his head. Wall bounce property.
:d::d::atk: - Rocky digs underground and ends up somewhere else. Functions like a ground-based teleport. :l: goes in front of opponent, :m: behind and :h: leaves you free to move underground for an extended time by holding down the button. Hyper cancellable.
:+:atk: [Air OK]
- Very quick command dash. Useable up to three times so long as it's in a different direction. Cancellable from normals.
"Eat tail, suckers!" - Assists
α Spitfire Twice
( :qcf::m:,:m: ) - Shoots two slow moving projectiles.
( :qcb::m: ) -"Shrapnel trap!" Rocky lays down a proximity mine that explodes into shrapnel near the opponent.
( :dp::h: ) - "Log trap!" Rocket ducks as a large log swings over his head. Wall bounce property.
"Incoming!" - Hyper Combos
Rock 'n' Roll
:qcf::atk:+:atk: - A flurry of Gatling gun shots that ends in an incredibly fast energy sphere that tracks the opponent. Mashable for more damage.
:qcb::atk:+:atk: - The spring trap. Sets a large trap on the ground that, on hit, springs the opponent into the air while doing damage. Usable as a combo extender. Rocket can set up to three Mad Hoppers out at a time. :l:+:m: bounces left, :m:+:h: bounces right, :l:+:h: bounces straight up.
:dp::atk:+:atk: - Rocket's level 3 Hyper Combo. Has OTG properties. Rocky buries the opponent underground and calls in an air strike as he jumps onto a helicopter to safety. Mashable for more damage. With meter, it can be followed up by Rock 'n' Roll.
For more information, check his UMVC3 Hyper Guide entry
Gameplay Footage and Other Media
Rocket Raccoon Hitbox Reference by FingerCramp
UMVC3 Rehab Guide by FingerCramp Jago