Rangda Bangda

Rangda Bangda (ランダ・バンダ) is the boss of the second Sigma stage of Mega Man X. It looks like a face in the background wall with moving eyes, a nose gun, and a mouth serving as a pit of spikes. To make matters worse, it can move its side walls inward to try and force X into the spiked pit. In Mega Man X, the best weapon to use is Chameleon Sting and Rolling Shield.

Rangda Bangda W
Rangda Bangda W is a modification that appears in Mega Man X5 with an Egyptian look and an Egyptian remix of the fortress boss music from Mega Man X. It's more difficult than the original Rangda Bangda. It has three eyes, each with a different color and attack, that appear one at time from one of the two eye cavities. The blue eye will move straight in the player's direction, the green eye will shoot, and the red eye will spread several projectiles in two directions. When the walls move to limit the player's movement, a small, miniature sunlike object will follow the player and spikes will appear in the floor, and sometimes in parts of the wall. It's recommended to use X with Gaea Armor against it. Rangda Bangda W, along with the boss that precedes directly before it, the Shadow Devil, are considered two of the hardest bosses in the entire Mega Man franchise. 

Trivia

 * In Mega Man Zero 4, a similar (though much smaller) robot, named Randam Bandam, appears in the second final stage. While similar in tactics to the X-series version, some players find its repetitive laughter much more annoying than the boss itself.
 * The first part of Rangda Bangda's name is the same as Rangda, a wicked witch of Balinese folklore who represented evil.