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 would like to see a new Heavy added, but that is not a Heavy WEAPON, but a Heavy SHIELD. Ideally it would act as a second health meter, or third if you are using Blessing of Light (or another over shield ability). Alternatively, it is an absolute immunity for "X" seconds, where "X" is equal to it's current ammo. Either idea would also have a "forcepush" bubble, kind of like a Titan's but instead it damages and throws enemies with whatever element the shield is, within it's AoE. Using this ability would use up all ammo in the heavy slot and you lose the shield.