"Come, Koma, and reclaim what you lost! Or does the great serpent fear a rematch?"

Fynn, the Fangbearer

Deathtouch
Whenever a creature you control with deathtouch deals combat damage to a player, that player gets two poison counters. (A player with ten or more poison counters loses the game.)

The List

Secret Lair Drop

Multiverse Legends

"I always said I had a score to settle with that serpent. I'm a man of my word."

Losing the game because a player (preferably an opponent) has ten or more poison counters is a rule of the game. Fynn doesn't have to still be on the battlefield when someone (preferably an opponent) gets their tenth poison counter.