If Blood Tribute is cast and kicked, the spell resolves by first making the targeted opponent lose half their life (rounded up), then — as part of the same resolution — you gain life equal to the life lost. That life gain will trigger Vito, Thorn of the Dusk Rose’s “Whenever you gain life” ability, causing the targeted opponent to lose that much life when the trigger resolves. If Blood Tribute is not kicked (or you gain 0 life), Vito will not trigger. See and for how life changes and life-gain triggers are treated, and Ruling [2024-11-08] about paying kicker as part of casting the spell.
Step 1
You cast Blood Tribute and (if you choose) pay its kicker cost by tapping an untapped Vampire you control; whether the spell is kicked is determined as part of casting the spell [Ruling 2024-11-08].
Step 2
Blood Tribute resolves. First the spell causes the targeted opponent to lose half their life, rounded up, and life totals are adjusted .
Step 3
As part of the same resolution, if the spell was kicked you gain life equal to the life lost this way; that life gain is an event that just occurred .
Step 4
Vito’s triggered ability watches for life-gain events and is treated as “Whenever a source causes you to gain life...” so Vito triggers from that life gain (unless the gain was 0) .
Step 5
The triggered ability is put on the stack. When that trigger resolves it causes the chosen opponent to lose that much life.
Step 6
The life lost from Vito’s trigger does not itself cause Vito to trigger again because Vito triggers on you gaining life, not on opponents losing life .
Resolution
When a kicked Blood Tribute resolves, the targeted opponent loses half their life (rounded up) and then you gain life equal to the life they lost. That life gain is an event that will cause Vito’s triggered ability to trigger (Vito’s “Whenever you gain life...” is treated as “Whenever a source causes you to gain life...”) . If the life gain is 0 (for example, because a replacement effect prevented the gain or the opponent lost 0 life), no Vito trigger occurs , , . Whether Blood Tribute was kicked is determined when you cast it (kicker is a cost paid as you cast the spell) [Ruling 2024-11-08].
