The Vitrolic Crux / Plague Maliwan Shotgun from Borderlands
Bring back S&S in general since we’re vissiting different worlds, gotta be a stockpile of them somewhere. The Orion could gice thr Lyuda a run for its money, theres the explosive Crux, and the Serpens AR. Could be part of some event / area with bosses and rare spawns that have increased chance to drop them, where you loot / raid some old S&S cache. (Or even do it fr Rhys so he can incorporate them into rebuilding Atlas after S&S seems to have gone under)
Oh, and maybe a Double Anarchy as a legend. Make it non-elemental obvious w/ really high bullet damage to set it apart from the Crossroads. (Most non-elemental SMGs arent even worth using over the Elemental optoons, they just dont do enough increased damage)
Oh, and the Elephant Gun, just because.