Mazirek, Kraul Death Priest turns sacrifices into +1/+1 counters, fueling a poison-and-drain engine where deathtouch creatures (Fynn, the Fangbearer and The Serpent Society) convert combat damage into poison counters while sacrifice outlets and death triggers (Bastion of Remembrance, Moldervine Reclamation) drain the table. The deck also runs The Gitrog Monster + Dakmor Salvage as a compact infinite self-mill combo that fills the graveyard to enable reanimation and card advantage.
Mazirek's counter engine: Whenever any player sacrifices a permanent, Mazirek puts a +1/+1 counter on each of your creatures. This scales with your sacrifice outlets—Viscera Seer, Reassembling Skeleton, and Yahenni, Undying Partisan all feed the counter machine while triggering death payoffs. Poison conversion: Fynn, the Fangbearer and The Serpent Society both have deathtouch; when they deal combat damage to a player, that player gets two poison counters (a player with ten or more poison counters loses the game). Mazirek's counters make these creatures larger and harder to block, accelerating the poison clock. Drain payoffs: Bastion of Remembrance and Moldervine Reclamation trigger whenever a creature dies, draining each opponent and gaining you life—each sacrifice or death event is a drain trigger. Graveyard engine: The Gitrog Monster + Dakmor Salvage creates infinite self-mill: during cleanup, you discard Dakmor Salvage and other cards down to hand size, The Gitrog Monster triggers to mill two cards and return Dakmor Salvage to your hand, and you repeat. This fills your graveyard with lands and creatures. Land recursion and ramp: Cultivate and Harrow, plus 2 more tutors find lands and trigger landfall payoffs. Tireless Tracker creates Clue tokens on each landfall, which you sacrifice for card draw and +1/+1 counters on Tireless Tracker itself. Evolution Sage proliferates (adds another counter of each kind already on a permanent) whenever a land enters, multiplying your counter growth. Compact kill: Michelangelo, Weirdness to 11 enters and creates a Mutagen token; its ability causes +1/+1 counters put on your creatures to be doubled (one counter becomes two). When combined with Bastion of Remembrance's drain trigger, the burst of token creation and counter doubling generates lethal damage or life loss.