+Scrap Princess asked what these potions did and this was my answer. I guess it was well liked enough that I want to put it here so I don't forget about it & I've tweaked some of the original post.
THERE ARE FOUR KINDS OF POTION...Each character consumes one of four potions. There are as many potions as there are characters. Nearby, you discover empty vials, some of which are broken, crushed. It's hard to guess how many others have consumed these potions.
...AND THEY WILL KILL YOU...All potions are lethal after 48 hours, though this final affect can be delayed an additional 48 hours if you consume the liver of someone who has also consumed one of these four potions (any of the four will do).
...UNLESS YOU DRINK ONE OF EACH.Consuming all four variety of potion (either directly or via liver) delays the final affect indefinitely. "Special affects" of consumption fade, with weird after affects persisting. Information to this affect will be relayed to the characters by a talking fox with two tails and seven eyes once the last potion is drunk. Or maybe they just know it to be true. Or maybe some creepy consigliere types lets them in on the situation. Flavour to taste.
THE POTIONSi. Blue Moon Jelly This is an exceedingly rare deep-sea creature. Consuming the creature grants you a rubbery consistency (you can't wear armour or bear heavy loads but you're immune to most bludgeoning damage). You are virtually immune to high-gravity affects and being above deep-sea pressure levels lets you leap incredible distances (like 50' horizontally and 30' vertically) by compressing your body and shooting away, like a spring. Your skin dries and cracks, longs for salt water and by the end of the second day you either die of dehydration or dissolve into sea water.
After affect: if this is the potion you first consumed and you manage to consume all other varieties before they kill you, you survive, but you are always cold, clammy, your hair hangs wet and you may add up to 10' to any distance you could otherwise jump and you take falling damage only after you've fallen 30' (ie, d6 for each ten after 30).
ii. The Frog Your knees snap and your leg joints invert. Your jawline joins your shoulders as your neck vanishes and your mouth grows enormous. You can dance across water and tree tops if unencumbered and you can swallow whole things half your size. Eventually, your mind fails, grows strange, hateful as your organs de-acclimate to this environment and you die, hyperventilating, suffocating on now-poisonous air, longing for steaming green jungles of a planet far, far from here.
After affect: if this is the potion you first consumed and you manage to consume all other varieties before they kill you, you survive, but you are never happy, always longing for a land you've never actually seen outside of dreams. Similarly stranded brothers and sisters will send you a map to a possible way home.
iii. The Shrimp Your eyes bulge, extend on stalks and you have all-around vision and wide spectrum vision. Your skin hardens and becomes chitinous You cannot wear armour but your skin counts as plate. You eat trash, smaller creatures, whatever you can find and you become strange, secretive. Eventually, your skin grows too heavy and gravity peels it from the flesh below, killing you in the process.
After affect: if this is the potion you first consumed and you manage to consume all other varieties before they kill you, you survive, but your skin is now translucent and your hair becomes a stiff and brittle mass, like coral. Your eyes remain larger-than normal and brilliantly-hued, and you retain wide-spectrum vision.
iv. The Fish You bud scales, gills and you can see and breathe underwater as on land. When under water, you can attack and evade by darting suddenly. Save v paralysis instead of rolling to hit or using your AC; attacks made in this way ignore armour and attacks avoided in this way deal no partial damage if missed and require no additional save for area/breath affect damage. Eventually, you can no longer breathe in water or land and die in a panic, asphyxiating, flopping.
After affect: if this is the potion you first consumed and you manage to consume all other varieties before they kill you, you survive, and you can breathe under water but you're totally hairless and you've got fluttering gills from the side of your face down to your nipples.