Thought I ask also if you can also pick what the primary element is so its not always frost, since if you pick fire as the secondary one, you basically have a double edge sword between the 2 elements for the entire save file like you just said. Plus, there are also enemies that resist frost at some point in the game, and I don't know why a save file can't draft from all elements and classes in the game, rather then be locked into 1 class and 2 elements, with one of them (frost) you'll always forced to take whether or you like it or not, and one (fire) is the double edge sword to it.
Also, for the Antidote Gel, I think the game said I did unlock it at the blacksmith, but the merchet never had it available after I unlocked it, nor does the game make it clear how you can use items on your own turn in combat since there's no "inventory" button that I saw in combat that lets you use consumables on your turn for free or for 1 action point.
As for his poison stacks, I think the amount he applies is reduced to 6 gems over 12, and the one skill that buffs its damage increases it by 1 and not 4, or only last for 1 turn. That's just my ideas.
Finally, there's no way to tell what the elements are weak or resist since there's no info on the UI screen to tell you an enemy's element and their resists and weakness, so how can someone know he's weak to fire if nothing on the UI tells you his element and there's no Pokemon type chart in the game to tell you "wood is weak to fire and resists water," especially when you aren't told your own character's element if you have some medallion that changes it and adds 2 weaknesses to yourself.
I hope that helps for feedback for now. Maybe I should wait until the game is finished in a few years or so to come back to it, but for balance patches, that boss is definitely one to look at since I don't know how other people are clearing it when you aren't using fire, and its confusing when the merchant even sells an antidote even after I think I unlocked it.