Be creative here there are no wrong ideas.
I would like the Spartan laser to be a weapon personally, just called something different "Charge Rifle" was a name I had in mind
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I want to see an exotic HMG that's a Gatling gun (a la Dust 514). As far as new weapon [i]types[/i]? I dunno. I saw flamethrower mentioned. That'd be sick, but it'd be hard to implement arc and void damage without it seeming like a stretch. Maybe some kind of energy mortar, sorta like the boomers and minotaurs have. It'd have to have a big magazine and large AoE to compete with RPGs though. Bows of any sort would be massively impractical in this game, and have no real benefit. There's not really a stealth component. A laser rifle would be interesting, but hard to balance. (If you've ever played Dust, you know what I mean) Honestly, I think Destiny has the right mix of weapons already.