Castle Crashing "The Beard"
Like Newgrounds Rumble, I don't quite understand why this game is on Kongregate. OK, it doesn't announce its origin right in its title, but the whole thing is essentially an extended Newgrounds joke -- apparently, Tom Fulp (the creator of Newgrounds) took a vow not to shave his beard until he finished his newest game, and so in this game, you have to battle a fearsomely enbearded Fulp for, uh, some reason.
The gameplay itself is like any boss fight from any 2-D platformer: you're tiny, and have a small weapon (which gradually powers up as the battle goes on), and Fulp is huge and has a wide variety of devastating attacks; defeating him requires learning his attack patterns and reacting accordingly, along with some degree of dexterity.
The presentation is high-quality: the art, sound, and music are all above-average, and the programming in the game is very solid. Still, there's just not much game here, and if you're not one to appreciate the joke, you won't get much value from that source, either. It's a fun little tidbit, though.