Mouse ATVs only appear once in each event of 'Sexy Kitten Yarngasm', they're fast so if you're unable to roll over one use your shockblast (Press
) to destroy it instead. They will appear on your map as with normal target enemies with a red square.
For me when playing in coop only the player who destroyed the mouse ATV earnt this, but it can unlock for the other person.
Here's what a Mouse ATV looks like, they'll be driven by mascots like usual.