Rangda Bangda (also called Ramba for short) is the boss of the second Sigma stage of Mega Man X1. It is the face in the background, and it has moving eyes, a nose gun, and its mouth is a pit of spikes. To make matters worse, it can move its walls inward to try to force X into the spikes. In Mega Man X1, the best weapon to use is Chameleon Sting.
Rangda Bangda also appears in Mega Man X5 with an Egyptian look and a Egyptian remix of the Mega Man X1 fortress boss music, and it's even harder at this point. X with Gaea Armor is a serious help here!
In Mega Man Zero 4, a similar (though WAY smaller) robot, named Random Bandom, appears in the second final stage. It's more annoying than Rangda Bangda because it won't stop laughing!