In Drifter's inventory, he will have four weekly bounties, one for each of the Gambit Prime armor sets (Invader, Reaper, Sentry, Collector). Each one requires you to complete a certain objective in Gambit Prime, and to make the highest-level motes you can, and wager them in the Reckoning, and successfully complete the run four times. When you complete your first of these bounties, your motes synthesizer will be upgraded, and you will be able to make level 2 motes, which require 2 synths each to make, and you will then be able to do Tier 2 Reckoning, where you can then wager those motes. You can then pick up another of the weekly bounties, and complete that by making and wagering level 2 motes, and finishing that bounty will upgrade the synthesizer again, unlocking level 3 motes, and Tier 3 Reckoning. Once you have Tier 3 unlocked, you can still do the weekly bounties, as those are the means to get the helmets for the different armor sets. Doing the same bounty multiple times will progressively unlock the +1, +2, and +3 versions of that set's helmet, and will unlock the +1 and +2 versions as possible Reckoning rewards, but the +3 versions can only be obtained by completing the weekly bounties.