I keep throwing them at the Hydragellos and they do nothing. No damage at all. They don't even show up in the battle text. They're supposed to be one-use but they... never actually get used up. Am I using them wrong or is this a glitch?

Preselection isn’t available for dark potions, pylonics, throwing vials, and shards so you have to click on them manually to use them during battle.

I don't use pre-selection, though. I go into battle. I chose my two weapons. I chose a spell. I make my turn. Then the site acts as if only the non-vial weapons and the spell exist.

battle images

Oh, I see. You have them in your armory instead of equipping them as potions. Take them out of your armory and equip them to your pet one by one through your inventory.

I see, thank you. Which raises the question of why I can put them in my armory if they're useless there, but that's another subject entirely.

They're not even available to put into the armory through the inventory so I'm guessing they can be quickstocked in because they have a tier assigned to them. That may be something Bug has to fix. They're intended for the 'potions' role, not 'weapons.'