Really Epic Punch

• WOTC Official Reminder Textofficial rules
  Fight — Each of those creatures deals damage equal to its power to the other.

• WWizards of the Coast2018-01-19
  Official Ruling
  The +2/+2 is permanent. It doesn’t wear off as the turn ends.
• WWizards of the Coast2018-01-19
  Official Ruling
  A combined host/augment creature will get +2/+2 because it has augment.
• WWizards of the Coast2018-01-19
  Official Ruling
  You must be able to target a creature you control and a creature you don’t control to cast Really Epic Punch. Note that you can target any creature you control, even if it isn’t a host or doesn’t have augment. It won’t get +2/+2, but it will still fight.

Rulings via Scryfall