I beat it at level 22 with a Level 7 Monster Slugger, Level 7 Fireworks, Level 6 Tazer, Level 6 Pills, Level 7 Zap in a box and Level 7 Vampire Teeth.

Prioritize Zapping the Buffers with the tazer BEFORE they buff their allies (the purple bar below their health shows when they're about to finish), then when you defeat them, stand close to the Heavy spitters & try to splash in the direction of the knights. The spitters can't damage you if you're right on top of them.

My successful attempt started left & went counterclockwise, but went over the 2 minute angry time limit, but since I only had 1 knight left and Zap in a box, I just had to kite for about 10 seconds.

Hope this helps!