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) where they act like regular Thwomps, though these Thwomps glow and wipe racers out if they run into them, unlike normal 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. Once again, racers will wipe out of they run into them

Mario Kart 8
Star Thwomps appear once more in Mario Kart 8 they are now light sparkled pink in the DLC Pack 1, though they act the same as before.