I made this a few years back, but it's fun enough to play for a little while.
The left knight is controlled as so:
a=block, s=jump, d=thrust, q=shoot
The right knight is controlled as so:
l=block, k=jump, j=thrust, o=shoot
I made it before most of those modern JS features rolled out, so it's a funny little game.
One day, it'd probably be fun to make PVP over WebRTC, but the latency would probably be a big issue.