Okay, since I got two codes, I thought I should offer up some of my spare codes too. After checking turns out I have way more than I thought I did. These are all pretty old, but if they were expired I think Humble would have said so.
2064: Read Only Memories [taken]
AI War: Fleet Command
Beat Hazard Ultra
Coffee Talk (US Switch) [taken]
Conan Exiles [taken]
Day of the Tentacle [taken]
Else Heart.Break()
The Escapists 2 [taken]
Girls Like Robots
Guacamelee Gold Edition
Guacamelee Super Turbo Championship Edition [taken]
Guns of Icarus Online
Hand of Fate [taken]
Human Resource Machine
Invisible, Inc. [taken]
Mini Metro
Monster Loves You
Mushroom 11
No Time to Explain
Nuclear Throne
Pathologic Classic HD [taken]
Potatoman Seeks the Troof
Rocketbirds: Hardboiled Chicken
Sproggiwood
Stronghold Crusader 2
Subnautica [taken]
Subsurface Circular
Super Galaxy Squadron EX
Super Hexagon [taken]
Super Meat Boy [taken]
The Surge [taken]
System Shock Pack (SS: Enhanced Edition and SS2) [taken]
Thirty Flights of Loving
Tower of Guns
Victor Vran [taken]
VVVVVV
World of Goo
Wuppo