So I have been thinking about different ways to involve these in my games (both online and at home) and after playing bioshock infinite I have figured out how (or at least how I am going to do it)
i also ran this idea in a game yesterday and i tested some of the bugs that i had with it (they did heaps of damage and ended up with heaps of uses) and i feel like i got rid of the various wrinkles that they had.
So you get the tonics/vigours/plasmid (here after referred to as potions or tonics) in your potion form, each potion is able to be only drunk once regardless of how many shots is in the potion (even if you decant it into a bigger bottle/vial and put more of the same potion in). a single tonic can only ever be drunk once and only one can ever be active on a person. When you drink the tonic you make a save vs poison/con save/fort save, if you pass you get your WIS modifier (im going to do a table for this) in uses of the tonic, if you fail you take 1D6 damage and get your WIS + INT modifier (im going to do a table for this) in uses. Each tonic does 2D4+level damage, and its elemental effects can cause other things to happen (like fire can light stuff on fire, lightning can short things out or shock things, etc etc), this is up to the gm of the game to decide how they want to implement the elemental effects of the tonic. if you drink a new tonic while you have one active the new one replaces the old one and you must make another save vs poision/con save/fort save and then you get the effects of the tonic you drank and no longer have the effects of the old one (unless you drank the same kind, then all you get is a refill as per the above for drinking)
If you couldn’t understand my stream of consciousness above I will try and streamline it down here
When you drink a tonic make a save vs poision/con save/fort save, if you pass you gain your WIS modifier (see below) in uses of the tonic, if you fail you take 1D6 damage and gain your WIS+INT modifier (see below) in uses of the tonic. The tonic does 2D4+level damage, and its elemental effects can cause other things to happen as per the type of tonic that it is (eg fireball can light stuff on fire), this final part is up to the GM of the game to decide how to run it.
ability score modifier
11 or below 1
22 or above 7
as all ways, let me know what you think and feel free to use this stuff for what ever you want