Infusion

Infusion is best picked up early-game, as it does not work retroactively, only adding health for every kill after receiving the item. It is possible to farm large amounts of health from certain stages, including all stages early-game and in Boar beach. The increase in max health per kill synchronizes well with Monster Tooth as on every kill not only will your maximum health increase but you will also heal. Infusion makes farming more attractive as it increases your chances, even though it can still be time consuming to do so.