| “ | Let the weeping sores of the lepers quench their thirst for war! | ” |
Lepers are the cheapest, toughest bodies available to anyone. They drop at 3 health for 2 coins with full retaliate, and can easily stonewall untargeted offense like Lead the Charge, Waylay, or ally-based attacks. They're also useful for anything that tallies health points such as Ritual Slaughter or Carnage. Unfortunately, they're a reactive piece, and in and of themselves, Lepers do nothing to help you win; they're reactive and synergetic, but make nothing happen in and of themselves.
They serve best as an early wall for sacrifice decks, saving you valuable life points in the first couple turns while you play your idols, then turning into a steady source of beefy bodies that can also be kept around as walls. The aforementioned Ritual Slaughter and Carnage make great use of its three life. Sacrificial Dais and Shrine of Rebirth will also increase its value incrementally.
Lepers suffer mainly from a lack of versatility; they exist to absorb hits and be sacrificed and have no other uses. Either you're running sacrifice and like Lepers, or you don't and never use them.