[Jotaku]

You might wonder how life stealing work in this game in either one of followings:
(1) total HP I obtain from life stealing = amount of HP inflicted to enemy + amount of HP stolen (% of my base damage), or (2) total HP I obtain from life stealing = amount of HP inflicted to enemy + amount of HP stolen (% of enemy's entire HP), or (3) I only inflict my base damage, and I get my life healed by %??? (% of enemy's entire HP), or (4) I only inflict my base damage and I get my life healed by %??? (% of my base damage)

Answer: (4) is correct. Life stealing simply comes last. The order for damage calculations is your base damage, then modifiers such as Extra base attack damage and crit, then it gets reduced by their modifiers, such as items like battlesuit or amazoness, then finally that damage dealt is then taken as a portion of lifesteal, so whatever the percentage your lifesteal is. Just so you know, omnisyphon works the same way.