You choose the target of the triggered ability as it goes on the stack, but you choose whether the creatures fight as that ability resolves.
05-10-2018
wotc
If the target creature is an illegal target when Affectionate Indrik's ability tries to resolve, the ability doesn't resolve. If Affectionate Indrik is no longer on the battlefield, the target creature won't deal or be dealt damage.
Random a card of Magic: The Gathering (MTG), but you can also roll the D20 dice, random a Planeswalker, have fun with the random rules and more.