While my normal approach to combat is to tank everything and smash whatever is in front of me (as well as detach my head and have it spam fireballs everywhere as it floats about), the knights always seem to dodge and I fear I'm becoming something of a joke. Even the ceiling collapses I cause fail to trap knights..but the biggest issue is something called blitz needle, which does so much damage to me that I just can't tank it.
What sort of guns would you suggest I craft to take on those pesky wolves I mean knights? I've currently got my eye on polaris, which would broaden my arsenal into shock (as well as fire), but permafroster seems like a good option as well.
Spiral Knights is primarily a game of dodging rather than tanking. Emulate the erratic dodging of gorgomegas and devilites. You can find videos of them on YouTube.
Meanwhile, successful strategies for offense include ranged attacks (rocket puppies, devilites), homing attacks (rocket puppies, gorgomegas), area attacks (some battlepods, mecha knights, Seerus), and freakishly fast movement (greavers, unfortunately hampered by ASI-6). So, yeah, some guns are a good idea. Shock really irritates knights, so consider Storm Driver, Polaris, or Overcharged Mixmaster. Skip the antigua-line guns, which are tedious to use, mediocre in damage, and poor in status.
At the risk of breaking my anonymity, I can say that I've played with you a few times. Your fire-tentacles attack could use some damage bonus or something. That thing works like 1% of the time. Also, try to aim your ceiling collapse to trap knights. If they're solo, then they're dead. Even if they're in a party, their friends are probably too oblivious to free them (e.g. microwaving a burrito in the middle of the fight).
Finally, Spiral Knights is much more fun when you play in a party. Those slag guards don't count; they're riding your coat tails. The Roarmulus Twins have been partying since they joined. Even the Snarbolax sometimes plays in a party. Don't be such a lone wolf.