I really like the description you gave

For the mysterious potion, I like the idea of using a combat dice, thanks!
Alternatively, I was maybe thinking of rolling 1D6 and determine any of the game system potions, what do you think ?
1 Potion of force
2 Healing potion
3 Heroic Brew
4 Holy water
5 Potion of speed
6 Poison !
For the dwarf beer, in my opinion you should have a chance to have a nasty effect due to the strenghtness of the beer. If you're a dwarf you may ignore the nasty effect. I like the idea that the beer could have the same effect as one of the game system spell, being in my opinion Rock skin and Courage.
Dwarven beer:Inside a small oak barrel circled of silver and closed with a big cork, you find a brown and bubbly liquid. You recognize it immediately due to its unique smell, it is the famous dwarven beer ! You can drink the beverage at any time and roll a die :
1-2 The beer has the same effect as Rock skin spell
3-4 The beer has the same effect as Courage spell
5-6 The beer is too strong for you and you pass your turn and lose 1 BP because you're drunk.
If you're a dwarf, you roll instead 1-3 ; 4-5 ; 6.