Mega Man 10: Part 1: Sheep Man Stage
Despite Bass being shown at the beginning at this video, you actually can't play as him until you beat the game, first. Before then, you can only choose between Mega Man and Proto Man. For now this will be a regular Mega Man run.
So let me start this playthrough off by going through the stage of this game's most infamous Robot Master: Sheep Man.
Before he caught Roboenza, he first herded sheep, then he worked in a circuit board manufacturer when he started collecting static in his wool. This would eventually lead to his main weapon: Thunder Wool.
His stage is pretty cool, though. Colored sections of the ground will disappear when you step on them. This also includes some spikes that will vanish with the normal tiles.
----------
Back on Sheep Man himself, he creates 4 clouds for his Thunder Wool attack, and the last of these four that strike with lightning will shoot out projectiles that travel along the ground before he appears again. Beat him, and that weapon is yours.
But alas, that's mainly why he's so infamous. Not just because of his design (despite the story of "Do Androids Dream of Electric Sheep?"), but because his weapon is annoying to use right. You shoot a cloud up into the air before it stops to strike down with lightning. This cloud can't be moved after it sets in place. So either your aim as to be JUST right, or you're facing enemies that just walk right into the lightning.
Also, you can't hit anything with the cloud, itself, or it will just disappear too early. What a waste that would be!