Currently, I own everything in the game apart from Iron Gamer Thor, Sentry Vulcan, Saci Ward Skin(is it only Latin servers?), and the Quetzaclcoatl Ward Skin. When I try to open a treasure chest it does the animation, but doesn't give me anything or consume the chest.
I'm pretty sure the two ward skins are through promos, and therefore unavailable. I did, however, get the Quetzacoatl ward in the PTS. Sentry is from levels in other Hi Rez games, and costs 300 gems. I'm not sure if its not available because its technically a promo, or if its because 300 gems skins weren't coded in since the rewards only show 400 and 600 gem skins. As far as I know, Iron Gamer Thor is just a 400 gem skin where profits go to Iron Gaming. It probably is given out to tournament winners or something, but wasn't sure if it was intended to be in chests or not.
TL;DR: Saci, Quetzalcoatl, Iron Gamer Thor, and Sentry Vulcan are unobtainable through chests.