Foe-Razer Regent

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

• WWizards of the Coast2015-02-25
  Official Ruling
  If the target creature you don’t control becomes an illegal target of the first triggered ability before it resolves, Foe-Razer Regent won’t fight and its last ability won’t trigger.
• WWizards of the Coast2015-02-25
  Official Ruling
  You choose the target of the first triggered ability as it goes on the stack, but you choose whether or not to fight as that ability resolves.
• WWizards of the Coast2015-02-25
  Official Ruling
  If a creature you control fights during an end step, the delayed triggered ability that puts +1/+1 counters on that creature won’t trigger until the beginning of the following turn’s end step.

Rulings via Scryfall