A player with ten or more poison counters loses the game. This is a state-based action and doesn't use the stack. In other words, it happens immediately and players can't respond to it, just like a player losing the game due to having 0 or less life.
Blightbelly Rat
If a creature with toxic deals combat damage to a creature or planeswalker, or if it deals noncombat damage, toxic has no effect and no player gets poison counters.
Conversely, replacement effects that apply to the number of counters put on a player can modify the counters placed this way. For example, Vorinclex, Monstrous Raider's last two abilities can apply to counters placed this way.
Magic: The Gathering · ™ & © Wizards of the Coast · Illus. Yeong-Hao Han
Card data via Scryfall. Rarix is fan-made; not endorsed by the rights holders.
