Suppose the bosses of Spiral Knights tried these matchups:
-A Roarmulus Turret (Spiral Knights) versus any of the Wily Machines from Mega Man. (If in doubt, go with Wily Machine 1. Or 9. 9 is cool.) Could any of the Wily Machine weapons pierce the Roarmulus Turret's heavy armor? Could the Roarmulus Turret aim and fire quick enough to keep up with the Wily Machine?
-Warmaster Seerus (Spiral Knights) versus any Fire Emblem boss. Obviously Seerus would rip apart the wimpy early-game bosses; we're not even considering them. But what about late game? His Rocket Hammer would count as an Axe in the Weapon triangle, while his Dark Retribution bombs would count as Dark in the Magic triangle; would this affect the boss's dodging, and would Seerus really care about the Weapon and Magic triangles in the first place? If so, that would definitely help Linus of FE7 with his Light Brand (a Sword (beats Axes) with a Light Magic special attack (beats Dark)). Would the battle be Spiral Knights based or Fire Emblem based? If the first, how do stats like Movement, Constitution, Skill and Speed translate to SK; if the second, what would Seerus's stats look like, and would his bombs have any range, or work like a Mine? Would Defense affect the Rocket Hammer's pure Elemental damage, or would it be solely based on Resistance?
If their armies fought, would the Gremlin technology prevail over the FE Boss's magi and flying troops? And how would statuses- Stun and Fire on Seerus's side, and Sleep, Berserk, Poison, and Silence on the FE side- factor in? If the boss used a poison weapon, would Seerus experience damage over time (the Fire Emblem poison effect) or weaker damage and healing immunity (the Spiral Knights poison effect)? Questions, questions...
Would the Royal Jelly tear up Giga Bowser? Would Lord Vanaduke survive a clash with Ganondorf? Who would win between the Snarbolax and the Lagiacrus of Monster Hunter Tri, or Pokemon's Arceus?
And shoot, I've only touched on Nintendo (Doc, you big ol' Nintendo geek, you); what about Sony's and Microsoft's nastiest bosses? How about other MMOs like World of Warcraft- would their own deadliest party-wipers pose a threat to Spiral Knights?
Feel free to ruminate further, but please don't start any cross fandom flame wars (Spiral Knights related or otherwise). And if this must go to Gremlin Chatter, let me know.
EDIT: Don't forget about Arkus, Razwog (when thinking of any famous early-game bosses), or Shadow Lair versions of bosses.
Ganondorf, Arceus > Gods, so they would win, plotwise.
We don't know how strong is the Swarm, but it would make an interesting cosmic collision Giygas vs the Swarm. xD