Agile

Agile (アジール) is one of the three X-Hunters in Mega Man X2. When you encounter him in one of the hidden rooms in the stages, he acts as his name implies--he moves very quick and wields a mean energy saber. Not only will he slash at you, but can create some large waves in a Shoryuken style upward swing. When you encounter him again in the third X-Hunter stage, he appears in a weird ship on top of the screen, creating spiked platforms that fall down to you (except for where his ship is), and also sends missiles at you occasionally. Magnet Mine is your best bet.

Agile has a short appearance in the opening scene of the PlayStation version of Mega Man X3, and one of Phoenix Magnion's attacks in Mega Man Zero 2 uses a image of Agile.

Trivia
Apart from the Giga Attack or the Magnet Mine, Agile's second form can only be attacked with the Shoryuken, which is conveniently hidden in his very stage. (edit: actually you can beat him with any of the weapons.)