Star Thwomp

Star Thwomps are a shiny variety version of Thwomps, these Thwomps only appear in Mario Kart games.

Super Mario Kart
Star Thwomps first appear in Super Mario Kart in Rainbow Road (SNES) they act like regular Thwomps except the only difference is that they glow unlike standard Thwomps.

Mario Kart 7
Star Thwomps reappear in Mario Kart 7 after a long absence they are colored light yellow instead glowing, they can create boost bumps when they hit the floor and only appear in the same track.

Mario Kart 8
Star Thwomps appear once more in Mario Kart 8 they are now light sparkled pink in the DLC Pack 1 nothing changed in there behavior at all.