The mini Janos (whose official name is unknown) are a variety of enemies that are encountered only in Rayman 2 and its remakes. They are dark-green one-eyed round monsters with skeletal arms that are found mostly in the Cave of Bad Dreams, which is guarded by their much larger counterpart, Jano, though another one appears at a certain point in the Sanctuary of Stone and Fire.
The first type of mini Janos attack by breathing fire, and they often attempt to avoid you when they look each other in the eye while attacking. Like Jano, they can dig underground, and they usually make their ambush at what seems to be a dead end, and there is usually more than one to defeat. If you get too close, they will eat you, so try not to get close.
The second type appears only once, and is characterised by a higher resistance and a different behaviour. Instead of breathing fire, this mini Jano hides behind columns, and only attacks you (by leaping on you and biting you) when you turn away. The only way to defeat this one is to wait until he pops out and gets close, turn toward him and shoot him as much as possible until he dies. And when you finally kill him, he drops a plum.
If mini Janos are met at a dead end, all of them need to be defeated in order to reveal a secret item, usually a plum or a Magic Sphere. The Mini Janos burp afterwords in the PS1 version cause their health bar lowers when you are being eaten, guess you don't taste very good.