Item Ideas

Egg Nest (Banjo-Kazooie)-A nest full of eggs that changes every half second. Depending on when you pick it depends on which egg you get.
Blue Egg-Nothing special, but it flies until it hits something.
Fire Egg-Very fast
Grenade Egg-Slow, but explodes.
Ice Egg-Freezes
Clockwork Kazooie Egg-Doesn't fly like the others but spawns a Clockwork Kazooie instead. It moves like a mecha-koopa, but lasts for 20 whole seconds. Its explosion is more powerful than one from a mecha-koopa.

Goomba's Shoe (Mario)-You get to bounce around and jump off of other fighter's heads for a little while.

Bag of Dragonite (EarthBound)-You turn into a dragon and breathe fire and claw at your foes. It lasts 15 seconds, and it is a more rare item.

I'm really liking the Egg Nest idea

Crystal Cluster/Crystal Shard (Freedom Planet)-A heavy object that, when broken, releases Crystal Shards that can be picked up, filling up the player's Final Smash bar. The Crystal Shards can spawn on their own, with Clusters being somewhat rare.

Was actually looking for a topic like this too, even if it is somewhat old

Wooden/Iron Sword (Legend of Zelda (NES)) The item is in it's original 8-bit form, with the ability to shoot a small beam, The beam will explode after two seconds and release 4 smaller beams that last for half a second. The Iron Sword is stronger than the wooden one

Cloaking Device (Melee)- Exactly the same as in Melee

1-UP (Freedom Planet)- A small head (Representing either Lilac, Carol, or Milla) that slowly bounces around the stage. Upon walking over it, it will start to spin around you, acting as a defensive hitbox. After a small while, it will sparkle and fly up and away, reducing your damage by 25% plus half of how much you started at (if you are at X%, you get healed by 25+X/2%) or 35 hit points if you are on Stamina Mode. However, taking even a small amount of damage before it begins to fly away will result in it being launched away from you, letting it be picked up by someone else. Sometimes, they can appear in a small cage that can be broken by attacking or throwing

Bonus Fruit (PAC-MAN)- Bonus items from PAC-MAN, each with the same effect as PAC-MAN's NSpecail from SSB4. There rarity is based on the fruit's "Position" in PAC-MAN's SSB4 move

Golden Gun (Goldeneye)- (Assuming 4th party items can appear) A projectile weapon that fires a single round. The round is extremely powerful and pierces shields and reflectors, but it has only one shot

A few more items:

OZ Kit (Borderlands Pre Sequel)- Gives your character an extra midair jump. This midair jump is somewhat weak, but it lowers your fall speed to almost none for about 2 seconds, allowing you to recover a large distance horizontally.

Grappling Hook (Legend of Zelda Wind Waker)- A long range battering item. It doesn't do much damage, but it does cause an above average amount of hitstun, allowing for some decent followups. It also gives you a tether recovery if you don't have one.

Creature Egg (Minecraft)- An item that will release a random enemy upon throwing, and behaves somewhat similarly to the Pokeball. The enemy spawned will be either a Zombie (Slow, but powerful), Skeleton (Ranged, but fragile), Spider (Fast, but weak), Creeper (Explodes), a Pig (The "Dud" of the group), Enderman (Not hostile until provoked, and teleports), Spider Jockey (Skeleton on a Spider), Ghast (Durable flying creature  that shoots explosives), Slime (A large enemy that splits down into 2 smaller, weaker slimes, which break into 2 even smaller, non-damaging slimes), and Witch (Throws de-buffing potions and damage-over-time). Skeletons, Zombies, and Spiders are common; Creepers, Pigs, Slimes, and Endermen are uncommon; Witch, Spider Jockey, and Ghast are rare. If left alone, the egg will release the creature, and it will be hostile to everyone (unless it is the Pig)

wheeled_tank wrote:

Creature Egg (Minecraft)- An item that will release a random enemy upon throwing, and behaves somewhat similarly to the Pokeball. The enemy spawned will be either a Zombie (Slow, but powerful), Skeleton (Ranged, but fragile), Spider (Fast, but weak), Creeper (Explodes), or a Pig (The "Dud" of the group). If left alone, the egg will release the creature, and it will be hostile to everyone (unless it is the Pig)

Could add the Enderman (Doesn't hurt anyone until provoked and can teleport), Slime (Comes in three sizes, the larger the more damage. Also when defeated spawns more slimes until smallest size), Ghast (Very hard to kill, flies and shoots explosives), and Spider Jockey (Super rare, combination of spider and skeleton).

Right. How did I forget the Enderman?! I'll make some edits to it when I get home

How about a Turret from Portal?

@DestinyIntwined

That's actually a good idea! I can imagine it acting like the Killer Eye in SSB4.