This is a 'Doppelgänger' of the Mushroom sprite. It looks like a normal mushroom until Mario approaches it. When he gets near, it comes alive and chases Mario, biting at him with sharp fangs! It cannot be jumped on, but a capespin, fire, or thrown shell/block will kill it.
Fixed sprite interaction with walls so now it can't pass through them. Improved "follow Mario" state so it doesn't rapidly flash between idle and attacking states. Optimized tilemap drawing routine and removed unnecessary code. Made the sprite hop when moving, making it look frenzier and more menacing. Added screenshot, tags and SA-1 support.