So we're all just going to ignore that Sceptile did not beat Darkrai 1v1 and was aided by the contributions of Heracross and Gible. And no. Dream Eater should not have fully restored Darkrai's health from the brink either (I'd estimate it'd be returned to about 50% before Gible fought it as well).
But this topic isn't asking if it can beat both Darkrai AND Latios, just if it can win a 1-on-1 with Darkrai.Ash-Greninja will not win against two legendary pokemon that is for sure. Never said Sceptile was an Arceus. It won with a critical hit from Leaf Blade and past experience.
Yeah, I'm annoyed that people still can't acknowledge that Darkrai took two super effective hits, a Megahorn from Heracross and a Rock Smash from Gible. Sceptile did finish him off, but without those attacks Darkrai probably would've swept Ash's entire team.