The Essence of Easymode is crafted with 1 Suspicious Looking Eye, 1 Worm Food, 1 Hornet Food, 1 The Beak, and 1 Old Skull at a Mythril Anvil.
Note that the Slime Crown and Guide Voodoo Doll are not required.
It used to be used in the creation of the Eye Of Oblivion, which is the boss summoner for the 2nd-to-final boss of the Avalon Mod. Although, it now is useless. It can still be crafted, though.
Though you can "use" this item in an active slot, it does not do anything, and it does not diminish if stacked.