Bliss is a rather fluorescent green and yellow pill. It appears to be sold in large amounts. Bliss is designed to cause an incredibly "blissed out", happy, euphoric feeling when ingested, and pain once withdrawal begins.
Linka is forced to fight a drug addiction to Bliss after her cousin, Boris, slips some pills into her food. Boris is already addicted to the pills when Linka visits, and he grows more and more desperate to keep himself in steady supply.
Boris dies of an overdose at the end of Mind Pollution.
Skumm's recipe is kept in a black notebook, but it and the remaining Bliss pills are destroyed by Captain Planet.
Skumm accidently poisons himself with the pills at the end of the episode, and it is assumed that he too must suffer through the pain of withdrawal, much like Linka.