With Dina, Soul Steeper and Exquisite Blood on the battlefield, a single event that causes you to gain life will cause Dina’s triggered ability to trigger, which makes each opponent lose 1 life, which in turn will trigger Exquisite Blood and cause you to gain that much life; that life gain will retrigger Dina, and the cycle repeats. Dina’s trigger is treated as “Whenever a source causes you to gain life,” per , and life totals are adjusted when effects cause life to change per .
Step 1
Some source causes you to gain life (this is a life-gain event that Dina’s ability responds to under ).
Step 2
Dina’s triggered ability triggers and goes on the stack; when it resolves, it causes each opponent to lose 1 life (and, per Ruling [2021-04-16], that is exactly 1 life per opponent regardless of how much you gained).
Step 3
Each opponent’s life loss creates a triggered ability from Exquisite Blood for each opponent who lost life; those Exquisite Blood triggers are put on the stack (one per opponent who lost life).
Step 4
When an Exquisite Blood trigger resolves, you gain life equal to the amount that opponent lost (typically 1); that life gain is a life-gain event that will cause Dina’s ability to trigger again under .
Step 5
Those new Dina triggers will resolve, causing each opponent to lose 1 life again, producing new Exquisite Blood triggers, and the cycle repeats.
Step 6
At the moment after any resolution that causes a player’s life total to become 0 or less, state-based actions will cause that player to lose the game immediately (checked per ) before any pending Exquisite Blood triggers can resolve, which can end the loop (see Ruling [2012-05-01]).
Resolution
These two cards form a repeating loop of triggered abilities: a life gain causes Dina to make each opponent lose 1 life, each such loss causes Exquisite Blood to trigger and make you gain life, and that gain retriggers Dina. Because Dina’s ability causes each opponent to lose exactly 1 life when it resolves (Ruling [2021-04-16]), each cycle subtracts 1 life from each opponent and then adds that much life to you via separate Exquisite Blood triggers. The loop continues until a stopping condition occurs (for example, an opponent’s life total becomes 0 or less, which causes them to lose the game via state-based actions before Exquisite Blood’s pending triggered abilities resolve, as noted in Ruling [2012-05-01] and under ).
