Minotaur Torch Hammer, Scorn lava launcher, Wretch naginata (the huge polearm they use), and HIVE BOOMER are just a handful of the weapons i would love to see brought up as either exotics or unique legendaries.
I also would like the scorn sniper rifle and sawblade launcher, and a Taken Phalanx shield (probably as a heavy "shotgun" that launches things similar to tractor cannon.
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Materials and parts would be better. Kill some hive, collect their metals, plasma etc and then use it to craft parts for your guns or modify your armour. The more of a material you use, the more the appearance and performance of your weapon or armour changes. Giving players a gunsmith type menu would be a great way to allow players to make their Guardian look more unique instead of just having preset armour.