Note: Potions are no longer in the game.
Potions are items that affect a player's feature (i.e. jumping) that first appeared to Beta users on October 10th, 2012. Now they are available to all players as of November 7th, 2012. You can only buy a max of 10 potions each, and once used, they are gone and need to be repurchased. As of October 31st, 2012, old worlds would have potions disabled by default and new worlds would have them enabled by default.
There are now commands to turn off a certain type of potion. Visit Chat Commands.
As of April 18th, 2015 potions have been removed.The effects and the auras got the potions' place in EE, like the Jump Potion becomes the Jump Effect.