Before Robert crushes my dreams in Discord, Ima post the list I compiled of possible ruined potion effects. I tried to make it so that the bad heavily outweighed the benefits, while usually being “harmless”. I have no idea the feasibility of most of these, so it’s only that, a list of possible inclusions if deemed fit. 
Inspired by the Deck of Many things in feel in a way.
I also wanted to differentiate between effects I felt the player should be given a hint to what they got from those that they would be given no information on by including a snippet of text that could be incorporated to what the player was thinking, somehow. Anyway here’s the list.
Good (10%)
“You feel rejuvenated.” Full heal
"You feel empowered." Stat boost
"As you drink the potion, you mind tingles. You get the feeling that you next attack will deal massive damage." Does not affect bosses, instantly kills most foes under level 20.
“You feel a slight spring in your step.” Player’s movement speed by 30% for X seconds
Player creates a lifewell at their current location.
“Your pockets feel heavier.” You find X-Y coins in your inventory! (Not a ton, maybe enough to buy a basic healing potion at the most.)
“You foresee future attacks against you.” You receive a premonition, granting you X% reduced damage for the next hour as you foresee attacks.
Potion has no discernible effect. (Upon receiving fatal damage, player is fully healed. Unlimited duration until activated.)
Potion has no discernible effect. (Player’s special bar fills twice as fast for 5 minutes.)
Neutral(80%)
“You feel funny, but cant quite place your finger on why.” Changes the color of the user’s skin for 1-X hour(s)
Polymorphs the player for 10-20 seconds
Player Shrinks to half their size.
Potion has no discernible effect. Nothing happens.
Potion has no discernible effect. (after a short duration, a fly flys by your ears every Y seconds for 1-X minutes)
“You see a dense fog roll in.” Player’s view distance reduced by 50% for X seconds
Players hands burst into harmless flames for 10 seconds.
“You feel an icy chill down your spine.” Player feels an icy chill, slowing the movement speed by 30% for X seconds
Player’s vision changes to Sepia for X minutes
Player’s vision changes to Monochromatic for X minutes
Player’s vision changes to Near-Infrared for X minutes (I.E, low light vision black and white)
Player’s vision changes to Inverted for X minutes
Player becomes invisible for X seconds
"The potion tastes disgusting, but you keep it down" Nothing happens.
“The potion tastes disgusting, but you keep it down”. The time until you can drink your next potion is doubled.
“The potion tastes disgusting, but you keep it down”. Hallucinations of enemies appear around others that only you can see.
“You hear faint whispers on the wind…” Allows you to hear the whispers of ancient beings for 10-30 seconds.
“Huh, that was apple cider, not a potion.” Nothing happens.
“You feel like you’ve gotten brighter! Wait a minute…” Player emits the Light spell for 1 minute.
Bad (10%)
Trigger a level 3 Arcane Explosion damaging all creatures and allies in range.
Teleport the player to a random portal location
Potion has no discernible effect. (Player is poisoned and will die in X period of time. I was thinking a week of actual time. The long game effect.)
Potion has no discernible effect. (Player’s next attack will generate increased aggro)
Potion has no discernible effect. (Player’s next X attacks do no damage.)
Potion has no discernible effect. (Player takes 10% more damage for the next hour)
Potion has no discernible effect. (The next standard potion drank will produce the opposite effect.)
"You feel a dark presence…"A dark cloud appears behind the player, moments later they die as the cloud dissipates. Cannot be resurrected.
“You feel time ebb and flow around you” Degrades a random piece of gear to broken.
“The potion tastes disgusting, but you keep it down.” You take 1% of your max health as damage every 2 seconds for 5 minutes, after 2 minutes. When the effect takes hold: “You feel darkness flowing through your veins.”
“The potion tastes disgusting, but you keep it down.” Your max HP is reduced by 25% for 6 hours.
“The potion tastes disgusting, and you cant keep it down. You suffer no damage, but your pride is badly hurt.”
It was fun making these so im gonna keep adding to a new list.