One or more shield counters on a permanent create a single replacement effect and a single prevention effect that protect the permanent. These effects are “If this permanent would be destroyed as the result of an effect, instead remove a shield counter from it” and “If damage would be dealt to this permanent, prevent that damage and remove a shield counter from it.” See rule 614, “Replacement Effects,” and rule 615, “Prevention Effects.”
April 29, 2022 · Streets of New Capenna
A shield counter on a permanent creates one replacement effect and one prevention effect that protect the permanent. These effects are “If this permanent would be destroyed as the result of an effect, instead remove a shield counter from it” and “If damage would be dealt to this permanent, prevent that damage and remove a shield counter from it.” See rule 614, “Replacement Effects,” and rule 615, “Prevention Effects.”
April 17, 2020 · Ikoria
The number of loyalty counters on a planeswalker on the battlefield indicates how much loyalty it has. A planeswalker with 0 loyalty is put into its owner’s graveyard as a state-based action. See rule 704.
July 12, 2019 · Core Set 2020
If a player has ten or more poison counters, that player loses the game as a state-based action. See rule 704. A player is “poisoned” if they have one or more poison counters. (See rule 810 for additional rules for Two-Headed Giant games.)