The Rocket Hammers are fun, yeah? I found them kinda enthralling as they allow you to behave like Seerus does, all leapin' around 'n' such. On that theme, I decided to spitball some other weapons that allow you to behave like the monsters that wield them. I limited myself to weapons that are wielded by the monsters, not part of them (that is, you won't find Greaver Gauntlets that allow you to wheel around like a drunken hummingbird and release a cloud of chaos to the four winds). I'm also no expert on game mechanics, so I shan't be giving any in-depth damage charts, only a thematic comparison to an existing weapon; if you wanna know what they look like go check the wiki. Anyhoo, here it is:

Phantom Sword (Blah)

Welp, may as well get this one over with first–oh yeah, akin to any boring three-swing sword in the game!
The charge attack is a swing like some weird middle ground between Divine Avenger and Gran Faust that shoots three low-graphics curse bullets that explode after a bit. Woop-de-do (Seems like it'd horn in on Faust's domain.)

Darkfang Thwack Hammer

Akin to the Rocket Hammer lineup. Thwackers have that smack-dash-swing pattern, which is exactly what I say for this slower-side weapon.
The first swing is a single-target hammer swing, the second is a dash that deals little (if any) damage, finishing with a swing like a Troika. The charge is a full spin, possibly akin to a Leviathan's. Dubbed "Darkfang" to distinguish from the wussy 1 star Troika reskin.

Ghostmane Razor

Akin to a Striker? I barely remember how these buggers attack. But however it is they do that, that's what the weapon does, and the charge flings some blades. (Sorry, I really called it in on that one, didn't I?)

Trojan Cleaver

Vaguely akin to the Troika line, or maybe the Rocket Hammer line. This weapon is all about knocking everything around with a two-'swing' combo.
The first action is a 5-square charge, dealing reasonable damage to anything in your way. The second is a Troika-like downward swing with a chance to stun (that does less damage than a similar-level Troika-line charge would do, for humanity's sake). The charge is a user-centric blast that pushes away all enemies with a chance at causing shock (no attack buffs for you, though). Every action would require a suitably-long lead-up, but would be hard to interrupt. Heavy armor would be recommended! (Also, to be consistent, all attacks would damage allies as well.)

Crusader Lance

Akin to... no, it's basically a shadowy Flourish, isn't it? Shadow/Piercing weapon? What'd that be good for? The rare Beast/Gremlin Complex?
Sorry, this'n's kind of a flop. Just wear Almirian gear with a Flourish an' you've got the same effect (provided you block after every combo).

Deadnaught Lance

In terms of heavy and slow, like the Troika line, I guess. A normal damage (to stay consistent, but piercing if we want to make any kind of sense) weapon with a two-strike combo. The first strike is a charge that takes a while to take off, but once it does carries you 5 spaces forward, mashing anything in your way. The first blends right into the second, which just continues the charge another 4 spaces; yes it carries you 9 spaces in a straight line. Look before you leap, as they say. The charge attack... uhmm... it, uh... REVIVES ALL FALLEN ALLIES. Really, I have no idea what could add to that. Deadnaughts are kinda one-trick zombies, aside from the resurrect thing. More charging? A charge charge attack?

Silkwing Silks (I'mbreakingmyonlyrulebecausewhereelseamIgoingtoshoehornthisideainandwhilewe'reonthesubjectthisisn'tevenaweapon)

A suit of armor granting a health boost to rival, nay, surpass that of Ancient plate, while at the same time greatly reducing your attack (wait, what) and also drawing the aggro of every monster on the field (uhh...). Hey, gotta know what it's like to be a Silkwing, right? (Incidentally, this is something Spiral Knight lead artist Ian McConville drew a while back, which I won't link to 'cuz I'm a jerk)

You may notice that I omitted some gremlin weapons, the reasons being:
A) We already have them (Demos' Deconstructors, Menders' Wrench Wands)
B) They behave totally differently from any player weapon (Scorchers: Brandish blast? Bullets? What is it?)
C) They're STUPID (Knockers, Mortafires)

Oh yes, and for the lazy (really now)
TL;DR: WEAPONS THAT BARF MAGMATIC RAINBOWS THAT DESTROY EVERYTHING ON THE FIELD AND YOUR PET

That was fun. Of course, these ideas should be taken with a pinch of salt (about enough to kill a giant colony), as they were developed by an antisocial knight who wants to strap a Combuster to his face to fire death beams like a Retrode.