YMMV / Babylon Five S 01 E 09 Deathwalker

• Complete Monster: Jha'Dur, known as Deathwalker, is a Dilgar war criminal and the worst example her species had to offer. Known for performing gruesome experiments upon innocents, Jha'Dur finds herself upon Babylon 5, and when cornered, she unveils a grand scheme to offer immortality to the other planets' governments. Earth accepts her offer and Deathwalker reveals to Commander Jeffrey Sinclair that immortality would require cannibalism, forcing civilizations to fall upon and destroy each other. The sheer delight she took in watching others suffer was nearly unmatched in the series.
• Fridge Logic: The serum requiring "the death of another living being" seems like it would be trivial to work around. Unless it's literally stealing somebody's soul (which is never remotely hinted at) you'd think any animal would do, and people still slaughter animals for meat in this setting. Even if it had to be humanoid for some reason, mindless clones are well within the technology of every race.