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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You said gun. I'm going to say Heavy Weapon slots definitely need new Melee weapons. That still needs heavy ammo to use, of course. The Blade of Crotas... Um blades, are nice. But imagine having a class of relic like weapons. I say a huge flail. Heavy Attack is a wind up shot that has some distance and can knock back even Phogoth, and can be aimed... Light attack is a wide swing. Jump attack has a nice smash. Honestly you guys want weapons. I want abilities though. Every class should have a sprint attack. A jump attack. Ability modifiers while super is charged while running, jumping. Warlocks and blade dancers can have a running blink instead of a slide. Gunslingers can have a area gun spin attack that automatically shoots.