Some Items that I think could work:
Mario Series:
1-Up Mushroom (stock only) = Gives one additional Stock
Super Leaf = Gives each fighter a Tanooki Tail that slows their fall if they press Jump in the air, and makes their jumps higher.
Spiny Blue Shell = Like in Mario Kart, it targets the foe in first place with high damage and major knockback. Very rare.
Donkey Kong:
Coconut Gun = Fires in Spurts. If it shoots ya, it's gonna hurt.
Animal Crate = Like Assist Trophies and Poke Balls, it gives an assistant. However, these are some of DK's buddies, such as Rambi, Squawks, Enguarde, ect.
Pikmin:
Bulbmin = In Pikmin 2, these were a cross between a Bulborb and Pikmin. You'd pick it up, and then throw it at foes. It chases after them for a short period of time trying to bite them.
Punch-Out!!
Headgear = Wearing this temporarily makes you take less damage.
Pokemon
Full Restore = That's right, a non-Poke Ball Pokemon item. Full Restore would fully heal your health, no matter the percentage.
Wow, this made me think of Hex...I wonder when he'll come back...