In a Two-Headed Giant game, poison counters are shared by the team. If more than one player on a team is chosen this way, only one of those players can be given an additional poison counter. The player who proliferates chooses which player that is. See rule 810, “Two-Headed Giant Variant.”
July 3, 2020 · Core Set 2021
Any time you have priority, you may turn a manifested permanent you control face up. This is a special action that doesn’t use the stack (see rule 116.2b). To do this, show all players that the card representing that permanent is a creature card and what that card’s mana cost is, pay that cost, then turn the permanent face up. The effect defining its characteristics while it was face down ends, and it regains its normal characteristics. (If the card representing that permanent isn’t a creature card or it doesn’t have a mana cost, it can’t be turned face up this way.)
September 30, 2016 · Kaladesh
rule 701.34b not present in this release
July 22, 2016 · Eldritch Moon
Only two cards belonging to the same meld pair can be melded. Tokens, cards that aren’t meld cards, or meld cards that don’t form a meld pair can’t be melded.