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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New heavy, a gears of war style torque bow with remote detonation. Like you'd be able to stick an enemy, wait till they are in a crowd and detonate so multiple adds are in the blast radius or say you stick a boss with 4 or 5 then blow them all at once causing a -blam!-load of damage :D