A Link to the Snitch said:
Out of boredom, what items would you like to see y'all?
One from each series:
Mario - Frog Suit. You pick it up and throw it at someone and it forces them to "run" by making short hops.
Zelda - Spinner. Ride it and do damage.
Kid Icarus - Bow and fire arrows. Self-explanatory.
Yoshi - Magic Dust. Used by Kamek; has the potential to make whoever it's used on either big or small, but can't be used on oneself.
Pokemon - Escape Rope. Pick it up and it slings itself over the character's shoulder; activate it by pressing B (or whatever) and it brings you back to the spot you first spawned at.
Kirby - Apple. Same as the one in Green Greens, but can appear in any level.
Star Fox - Twin Laser. Doubles the damage of your projectiles (B moves only) for a short time. If you don't have any, too bad. >_> Projectile users need something going in their favor when items are turned on.
Metroid - Grappling Beam. "Throw" it and it'll pull the enemy toward you, not for a throw but to set up any other kind of combo.
F-Zero - Speed Bomb. Attaches itself to the other player; if at any time they stop moving, it explodes. (Taken from that one F-Zero GX chapter.)
Donkey Kong - Squitter, Squawk, or Rambi as an assist trophy. They attack enemies.
Animal Crossing - Bee Swarm. Take a wild guess what it does.
Fire Emblem - Angelic Robe. Until you die, you (and only you) start taking knockback as if the damage ratio were 0.9. (If you get two, it goes down to 0.8.)
Mother - Skip Sandwich. Eat it to recover 6 HP and double ground movement speed (only ground movement) for a short period of time.
Nintendo DS - Nintendo DS Lite. It opens up and tinkers with the game, adjusting the brightness and volume and the players' names, then is forced to shut down to save its settings.
If I left a series off the list, it's because either it hasn't been confirmed yet or I couldn't think of anything.