Like in any other SSBB game, SSBO contains a variety of items that have different characteristics. While some items are for summoning a fighter, others are used for battering.
Assist Trophy (Summons a fighter to help you)
Back Shield (Protects you from incoming attacks from behind.)
Banana Juice (Recovers 50% damage)
Banana Peel (Throw it on the ground so fighters would slip when they step on them)
Barrels (Throw and carry it around to reveal an item)
Beam Sword (A blade consisting of pure energy. Use this blade to slash opponents)
Beehive (Throw it on a fighter so they get stung by a swarm of bees)
Beetle (Activate this, so it can grab a fighter to deliver it into the sky)
Blast Box (Don't use fire attacks on it, or else it will explode)
Blast Mask (Wear it on your face. When someone tries to punch you, you'll blow up)
Bob-Omb (Walks around the stage for a short time, then explodes)
Bombchu (Walks faster tha a Bob-omb. Even able to crawl under the stage)
Boomerang (Throw it on fighters to bring them to you)
Boss Galaga (An extraterrestrial that rescues fighters from the blast zone)
Bullet Bill (Become a Bullet Bill and speed through the stage)
Bumper (When you go into this, you will be launched backwards)
Bunny Hood (Wear it over your head and speed around the stage)
Capsule (Contains something)
CD (Collect one to expand your jukebox)
Cracker Launcher (Fires crackers upwards into opponents)
Crates (Some crates also have wheels. Use this to avoid incoming attacks)
Cucco (It's a chicken, but don't anger it!)
Custom Parts (Contains some bonus elements for the Sandbox Mode)
Daybreak (Collect all the pieces and blast your opponent away)
Deku Nut (After being thrown, these nuts explode and will paralyze your opponent)
Double Cherry (Eat this rare fruit and you have a duplicate of yourself)
Dragoon (Gather all the parts to divebomb into your opponent)
Drill Arm (Let the opponents taste your drill)
Eggplant Bomb (Turns a fighter into an eggplant for a short time, but with legs)
Fairy Bottle (This fairy will recover your entire damage if you free him)
Fan (A simple paper fan. Deals little to no damage when used)
Fire Bar (Similar to the Beam Sword, but with fireballs forming the blade)
Fire Flower (Pick up this flower to spout flames on your opponent)
Fishing Rod (Throw the line to snatch opponents from far away)
Food (Recovers a fair amount of damage, depending on the food item)
Franklin Badge (Reflects attacks when worn)
Freezie (When thrown, opponents will be frozen solid)
Golden Hammer (Fighters who wield this hammer will wreck faster than with a normal hammer)
Gooey Bomb (An explosive covered in sticky slime. Latch it into a fighter so they wouldn't know the danger)
Green Shell (A shell that can be thrown)
Gust Bellows (Blow your opponents away with a breeze)
Hammer (Wreck forward to bash opponents into the Blast Zone)
Heart Container (Recovers the entire damage)
Hocotate Bomb (Launch it into the sky, then it explodes while landing on the stage)
Home-Run Bat (Bash your opponents with full force, as if they were a Sandbag)
Hothead (Moves around the stage to burn opponents who stand on their way)
Jupiter Djinn (One of the Djinns that use a wind-based attack)
Killer Eye (This eye fires laser beams to electrify your opponents)
Lantern (Carry it around. When punching, it begins to flicker)
Lightning Bolt (Shrinks all the fighters on the stage)
Lip's Stick (Plant a flower on your opponent's head after being hit by this stick)
Mars Djinn (A Djinn that uses Fire-based attacks)
Master Ball (Summon an extremely powerful Pokémon)
Matryoshka Doll (Consists of three dolls, with the final third containing a random item)
Maxim Tomato (Eat this juicy tomato to recover 100% damage)
Mercury Djinn (This Djinn will use its Water attacks to make your opponent wet)
Metal Box (After coming in contact with the box, you will be encased in metal)
Motion-Sensor Bomb (Plant it onto surfaces, but explodes when approaching)
Mr. Saturn (Throw it around)
Ore Club (Swing this massice club to create gusts)
Pitfall (Throw it onto a fighter to bury them onto the ground)
Poison Cloud (Emits a poison gas that damages all fighters on the stage)
Poison Mushroom (After being eaten, the fighter will be shrunk into the size of an ant)
PokéBall (Summon a Pokémon to attack fighters)
Potted Piranha Plant (Gnaws on opponents who approached it too close)
POW Block (Creates an earthquake to blast everything away)
Rare Candy (Boosts your stats. Works similar to the Super Star, but without the invincibility)
Ray Gun (Fire a laser beam)
Rocket Belt (Fly around while you are wearing this item on your back)
Sandbag (No matter how hard you attack, it will spawn some precious items)
Screw Attack (Wear it and perform a Screw Attack move)
Smart Bomb (Creates a massive explosion after being thrown)
Smash Ball (Grab the Smash Ball to unleash your Final Smash)
Smash Coins & Bills (The currency of Smash. Can be earned in various game modes)
Smoke Ball (Covers the stage in thick smoke after being thrown)
Soccer Ball (Kick it around to launch it forward)
Special Flag (Grab this flag to recover yourself)
Spiny Shell (Creates a big, blue explosion after hitting the ground)
Spring (Jump on it to launch yourself. Can be thrown to drive fighters off the stage)
Sprinkler (Activate it and the stage will be covered in ink)
Stamp (A small illustration showing something)
Star Rod (Launch a flurry of stars while using it)
Stealth Suit (Makes fighters invisible for a short amount of time)
Steel Diver (Fires mini-torpedos)
Super Bell (Fighters will wear a cat costume which doubles the speed)
Super Horn (While activating, it creates a loud noise to deafen your opponents)
Super Leaf (Gives fighters raccoon ears and a tail. Also makes you levitate after jumping)
Super Mushroom (Eat this mushroom and you will grow into a giant)
Super Scope (Fires a flurry of small fireballs)
Super Star (Become invincible after grabbing the Star)
Superspicy Curry (After eating this spicy dish, you will spout flames all over yourself)
Team Healer (Heals damaged opponents in team battles)
Timed Dynamite (Throw it before it explodes)
Timer (Slows the world around you)
Toy Hammer (Deals less damage than a regular hammer)
Trophy (A figurine which showcases something random)
Unira (This creature has retractable spikes. After being attacked, it will expand its spikes)
Venus Djinn (Uses an Earth-based attack)
Warp Star (Grab onto it, but the star will bring you back to the stage, resulting into a small explosion)
X Bomb (Creates a cross-shaped explosion)