Either give it a catalyst with a unique perk or give it barrel constrictor, that would work pretty good with the exotic perk where you have to hit most pellets to proc the freeze/ignition. :>
#conditionalfinality
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I think a catalyst they could add that wouldn't be too strong is increase reload and require less pellets exclusively in pve. But in its current state anything other than that would probably result in bungie nerfing the weapon more than the catalyst even helps.