Ash-Greninja's
Destructo Disc Giant Orange Water Shuriken vs Alain's Mega Charizard X. While it's really disappointing that such a prolific, amazing and stunning looking move ended up in a failure and not of much significance in the course of the fight from Ash's perspective, judging from the visual implication of the collision of MCX's final Blast Burn and Orange Shuriken it is reasonable to assume that both of the two finisher moves roughly had a similar amount of power, because the collision of the two moves looked like pretty much equal/stalemate. The fiery part (which was obviously created via Blast Burn) and the watery part of the explosion (which was obviously created via Orange Shuriken) were roughly equal in terms of size and after the energy impact of the explosion part was over, if the examine the smoke clouds of the explosion, the black part of the smoke cloud and the while part of the smoke cloud were depicted as almost absolutely equal in size, which further indicates that the power of the two final finisher moves of MCX and A-G which caused that gigantic explosion, were more of less, roughly equal in power.
The reason of MCX still coming out on top after that huge explosion despite the explosion pretty much being a stalemate can be accustomed to MCX having way more physical endurance and resistance compared to A-G, so it was able to endure that enormous impact of that explosion and still remain standing, with A-G was unable to do.
And of course, judging power scaling wise, the strongest depicted finisher move ever used by a Pokemon of MCX's calibre (who would be E4 Mega Ace level +) in the series, which MCX's final Blast Burn was, an all-out attack consuming almost the entire battlefield, would obviously be significantly/far more stronger than any other strong move used by GPCISS (Ash's Top 6 strongest Pokemon) in the anime thus far. So being roughly equal (or close to being) in power with MCX's final Blast Burn makes Ash-Greninja's Giant Orange Water Shuriken easily and by far the strongest move used by an Ash Pokemon so far in the anime.
All hail Ikuzefrog!!!