Edge cases: state-based actions and copies

State-based actions are checks the game makes whenever a player would get priority, so between spells and abilities, never while one resolves. They all happen at once:

• a creature with 0 or less toughness goes to the graveyard
• a creature with damage at least equal to its toughness is destroyed
• a player at 0 or less life loses
• a +1/+1 counter and a -1/-1 counter on the same permanent are removed in pairs