Keeper of Fables

• WWizards of the Coast2019-10-04
  Official Ruling
  Keeper of Fables's ability triggers even if it's dealt lethal damage at the same time that non-Humans you control deal combat damage to a player.
• WWizards of the Coast2019-10-04
  Official Ruling
  If non-Human creatures you control deal combat damage to two or more players at the same time, Keeper of Fables's ability triggers for each of those players.
• WWizards of the Coast2019-10-04
  Official Ruling
  Because creatures with first strike deal combat damage before creatures without first strike, Keeper of Fables's ability can trigger twice during one combat if your creatures deal combat damage to one player at different times.

Rulings via Scryfall