Needs a Better Title. Up for Grabs. This appears predominantly in Platform Games. It's a creature that looks perfectly cute and innocuous while your character on-screen is facing it. Possibly it even looks like a rock or other terrain feature as camouflage. Then, if you turn your back on it, it'll move forward and attack you when it gets close enough - unless you turn back to face it, in which case it goes back to looking innocent. For example,
Hello, Unknown Troper. You'll need to get known to lend a hand here.