The Power Within: Part 2 - S3-E48
Plot hole: Jaden activates Super Polymerization to fuse Elemental Hero Neos and Rainbow Dark Dragon to summon Rainbow Neos. Where exactly did Rainbow Neos come from? All the cards used in the Yu-Gi-Oh universe come from companies that developed them and the Rainbow Dragon card was only first made earlier in the season, so there's no way a monster that requires Rainbow Dragon as a Fusion material monster would exist. (00:17:43 - 00:18:43)