HP Absorption

HP Drain is simply damage dealt to the enemy along with HP recovered to the attacker proportional to the dealt to the enemy rounded-down. The skill of which uses Lifesteal Attack will always use the base element of the unit or enemy using it.

HP Drain attacks that deal 1 damage will recover 0 HP.

HP Drain works exactly like Lifesteal Damage.

Formula
HP Recovered = Damage Dealt * HP Drain Effect (%)

For example, Bitter Manipulator Zora, whose HP Drain Effect has a 20% chance of recovering 20-25% of damage dealt as HP, dealing 100,000 damage will recover any amount of HP between 20,000 and 25,000, provided that the HP Drain Effect activates.