Extort (Whenever you cast a spell, you may pay . If you do, each opponent loses 1 life and you gain that much life.)
At the beginning of each of your postcombat main phases, if you gained 3 or more life this turn, exile Sorin, then return him to the battlefield transformed under his owner's control.
Extort (Whenever you cast a spell, you may pay . If you do, each opponent loses 1 life and you gain that much life.)
+2: Create a Food token.
−1: Sorin deals damage equal to the amount of life you gained this turn to any target.
−6: Gain control of target creature. It becomes a Vampire in addition to its other types. Put a lifelink counter on it if you control a white permanent other than that creature or Sorin.
Cast Sorin as a 2-mana lifelinking, extorting creature, then trigger lifegain to flip him into a planeswalker the same turn. From there grind value with Food, machine-gun opponents with the -1 based on life gained, and lean on lifegain payoffs and aristocrats to drain the table. He plays as a low-curve midrange engine that snowballs incremental life into damage and card advantage.
Two-mana commander that flips into a powerful planeswalker, giving huge value for cost
Lifelink plus Extort makes lifegain triggers trivial to hit reliably
The -1 scales into a repeatable removal/burn engine when you stack lifegain
Strong BW color identity for removal, recursion, and aristocrats
Front-side is a fragile 2/3-ish creature vulnerable to removal before flipping
-1 does nothing if you haven't gained life that turn, so it's setup-dependent
No card draw or ramp baked in; relies on the rest of the deck
Planeswalker side is a target for attacks and can be raced in aggressive pods
Legendary Creature — Human Noble // Legendary Planeswalker — Sorin
. If you do, each opponent loses 1 life and you gain that much life.)