Simple but efficient idea, as an Isaac player this instantly triggered by Isaac reflexes!
I'd have just added a way to see our stats values (like in Isaac) and pushing a bit on his dialogue that Mr Goblin isn't exactly sure of his work. "Huh, I think the yellow potion is good? The green one is probably bad..."
Also, the conditions to get healed and the effects of leveling up are not very obvious from the player's perspective
Still, I had a lot of funs playing it!