TheWanderingMist
Paladin of the Snow Queen
That line right there reminds me of the classic shounen anime setup: a strong opponent who prides himself being undefeated is, in the end, defeated by the (often seemingly weak) protagonist. I'm not saying Ash and his Litten will defeat the Masked Royal and his Incineroar, but I'm not ruling out the possibility, either.
It's a 4 way battle, so someone else could end up defeating him after Litten weakens Incineroar.