Ghost (Find Mii)
From the Super Mario Wiki
Ghosts are enemies that appeared in the StreetPass Mii Plaza game, Find Mii. The Ghosts that appear in Super Smash Bros. for Nintendo 3DS as Smash Run enemies hold shields that can block hits and reflect projectiles. Ghosts follow the player, hovering in front of the character. They can be only attacked by hitting their top, bottom, and behind, and they can be grabbed and thrown.
Super Smash Bros. for Nintendo 3DS Trophy information