Revenant Flesh

 is obtained by killing the Revenant Horror. It is a drop, and is used to make items like the Revenant Viscera, Wands etc. (Occasionally, the game refuses to let you craft with this item. All you need to do is go to Maddox, click Boss Leveling Rewards, and claim them)

Many high level items are crafted with Revenant Viscera, which must itself be crafted with Revenant Flesh.

In a scam, this item is disguised as Enchanted Rotten Flesh, which is worth much more. Scammers put Revenant Flesh in a backpack, passing it off for the more expensive Enchanted Rotten Flesh, and asking unsuspecting players to give collateral for the "Enchanted Rotten Flesh", because the player "needs someone to craft Zombie Hearts". Then, after the unsuspecting player gives collateral, they run off with the money.