Haze Frog

• WOTC Official Reminder Textofficial rules
  Flash — You may cast this spell any time you could cast an instant.

• WWizards of the Coast2010-06-15
  Official Ruling
  If two Haze Frogs enter during the same turn, each one's ability will prevent the other one's combat damage.
• WWizards of the Coast2010-06-15
  Official Ruling
  Combat damage dealt by Haze Frog itself during the turn it enters isn't prevented. Combat damage that would be dealt by all other creatures is prevented, including creatures that weren't on the battlefield at the time the ability resolved.

Rulings via Scryfall