Rule 810.10 · Two-Headed Giant Variant
Effects that cause players to get poison counters happen to each player individually. The poison counters are shared by the team.
Subrules
If an effect needs to know how many poison counters an individual player has, that effect uses the number of poison counters that player’s team has. If an effect needs to know how many poison counters a player’s opponents have, that effect uses the number of poison counters opposing teams have.
If an effect says that a player loses poison counters, that player’s team loses that many poison counters.
If an effect says that a player can’t get poison counters, no player on that player’s team can get poison counters.
If a rule or effect needs to know what kinds of counters an individual player has, that effect uses the kinds of counters that player has and the kinds of counters that player’s team has. A player is “poisoned” if that player’s team has one or more poison counters.