If a player has 0 or less life, that player loses the game as a state-based action. See rule 704.
May 3, 2019 · War of the Spark
Damage marked on a creature remains until the cleanup step, even if that permanent stops being a creature. If the total damage marked on a creature is greater than or equal to its toughness, that creature has been dealt lethal damage and is destroyed as a state-based action (see rule 704). All damage marked on a permanent is removed when it regenerates (see rule 701.14, “Regenerate”) and during the cleanup step (see rule 514.2).
January 25, 2019 · Ravnica Allegiance
Damage marked on a creature remains until the cleanup step, even if that permanent stops being a creature. If the total damage marked on a creature is greater than or equal to its toughness, that creature has been dealt lethal damage and is destroyed as a state-based action (see rule 704). All damage marked on a permanent is removed when it regenerates (see rule 701.14, "Regenerate") and during the cleanup step (see rule 514.2).
April 27, 2018 · Dominaria
Damage marked on a creature remains until the cleanup step, even if that permanent stops being a creature. If the total damage marked on a creature is greater than or equal to its toughness, that creature has been dealt lethal damage and is destroyed as a state-based action (see rule 704). All damage marked on a permanent is removed when it regenerates (see rule 701.14, “Regenerate”) and during the cleanup step (see rule 514.2).
September 30, 2016 · Kaladesh
Damage marked on a creature remains until the cleanup step, even if that permanent stops being a creature. If the total damage marked on a creature is greater than or equal to its toughness, that creature has been dealt lethal damage and is destroyed as a state-based action (see rule 704). All damage marked on a permanent is removed when it regenerates (see rule 701.13, “Regenerate”) and during the cleanup step (see rule 514.2).
May 1, 2014 · Journey into Nyx
Damage marked on a creature remains until the cleanup step, even if that permanent stops being a creature. If the total damage marked on a creature is greater than or equal to its toughness, that creature has been dealt lethal damage and is destroyed as a state-based action (see rule 704). All damage marked on a permanent is removed when it regenerates (see rule 701.12, “Regenerate”) and during the cleanup step (see rule 514.2).
September 30, 2011 · Innistrad
Damage marked on a creature remains until the cleanup step, even if that permanent stops being a creature. If the total damage marked on a creature is greater than or equal to its toughness, that creature has been dealt lethal damage and is destroyed as a state-based action (see rule 704). All damage marked on a permanent is removed when it regenerates (see rule 701.12, "Regenerate") and during the cleanup step (see rule 514.2).
June 17, 2011 · Commander 2011
Damage marked on a creature remains until the cleanup step, even if that permanent stops being
April 1, 2011 · Duel Decks: Knights vs. Dragons
Damage marked on a creature remains until the cleanup step, even if that permanent stops being a creature. If the total damage marked on a creature is greater than or equal to its toughness, that creature has been dealt lethal damage and is destroyed as a state-based action (see rule 704). All damage marked on a permanent is removed when it regenerates (see rule 701.11, "Regenerate") and during the cleanup step (see rule 514.2).
February 4, 2011 · Mirrodin Besieged
Damage marked on a creature remains until the cleanup step, even if that permanent stops being a creature. If the total damage marked on a creature is greater than or equal to its toughness, that creature has been dealt lethal damage and is destroyed as a state-based action (see rule 704). All damage marked on a permanent is removed when it regenerates (see rule 701.11, “Regenerate”) and during the cleanup step (see rule 514.2).
October 1, 2010 · Scars of Mirrodin
Damage marked on a creature remains until the cleanup step, even if that permanent stops being
July 16, 2010 · Magic 2011
Damage marked on a creature remains until the cleanup step, even if that permanent stops being a creature. If the total damage marked on a creature is greater than or equal to its toughness, that creature has been dealt lethal damage and is destroyed as a state-based action (see rule 704). All damage marked on a permanent is removed when it regenerates (see rule 701.11, "Regenerate") and during the cleanup step (see rule 514.2).