For each day Xur is available, he has different Perks on the weapons he offers, like Banshee offers, including Hawkmoon & DMT, and also different stats on the gear. And maybe on the last day he's available before reset, you're allowed to spend double currency with Exotic Cipher & Ascendant Alloy (3 for Hawk/DMT) to actually choose which Perks you want, similar to Crafting. And Triple currency with Exotic Cipher & 3 Ascendant Shards (6 for Exotics) on gear, physically changing the stats, but cannot go above 25 or below 2 for a stat & cannot go pass total overall stat points of that piece offered for the day I know you can find dropped gear that has 0 or above 25 for a stat, I mean I've seen or found gear with 32 in a stat, but in order to balance this mechanic out, stats should be capped 2-25, maybe 20. Can only choose ONE Legend gear OR up to ONE Legend weapons OR 1 Exotic a week. So if you choose Hawk/DMT or Exotic gear, you cannot also choose the Legendary loot, and vice-versa, and either 1 Legend gear or weapon. Also Xur should only offer older non-sunset weapons & gear that do not dropped anymore, but with updated Intrinsic & Origin Perks