From the Super Mario Wiki
Not to be confused with Unera
A Unira is an item in Super Smash Bros. Brawl, coming from the game Clu Clu Land. It is a type of Sea Urchin encountered in the said game, acting as an enemy. In fact, it has been referred to as a Sea Urchin in other English localizations, but is known under its Japanese name in Super Smash Bros. Brawl. In Super Smash Bros. Brawl, the Unira can be picked up and tossed at opposing players. After being thrown, its spikes pop out damaging all except the one who threw it. When players stand close enough to it, it draws them toward itself. The Unira later appears in Super Smash Bros. for Nintendo 3DS, and later will appear in Super Smash Bros. for Wii U, having the same effect as in the previous installment.
A Unira can change "possession", so to speak, if it is attacked. For example, if a player throws it, the Unira will not harm the player; however, if an opponent attacks the Unira, its properties will change and cause harm to the player while not damaging the opponent.
Unira are also seen in WarioWare: Twisted!, in the microgame Clu Clu Land, and in WarioWare: Smooth Moves, which features another microgame of the same name.
Trophy information from Super Smash Bros. Brawl
||NES Clu Clu Land
||In Clu Clu Land, the Unira hid gold ingots in an underwater maze, then tried to stop Bubbles from getting them. In Super Smash Bros. Brawl, you can attack an Unira to send it bouncing away. Any fighter it hits will go sprawling. If it hits a wall, it'll bounce back, and if you hit it with a powerful attack, it will transfer the attack to whomever it hits and launch them.
Names in other languages
||From "pungere" (to sting) and an alterate form of "fissare" (to fix, to attach)