Swaphopper is an enemy that appears in Super Mario Galaxy 2.
They have a big spike on their head, so if Mario or Luigi jump on them they will get hurt. They jump sideways and are always in Mario or Luigi's direction. They are invincible until Mario or Luigi hits a Gravity Switch, and the Swaphopper's head and spike will be upside-down. Jump on them when the head is upside-down and they will be defeated.