Flamemon X4 strike now! is the 21st episode of Super Digimon Xros Wars.
Blue Xros Heart and Solar Flare chose to retreat for now to regroup and think of a plan of action. The next day the 2 armies team up to fight the Dark Knight Army. Ian sends Flamemon X4 to fight and Ryo sends MetalGreymon. Ian then tells Ryo that if they don't work as a perfect team they'll lose, Ryo says that they need to battle like they did back in the Bug Zone. Then Ian activates a DigiMemory and Ryo Digi-Xroses Cyberdramon with MetalGreymon. After that DarkKnightmon uses the Darkness Loader and Digi-Xroses himself with SkullGreymon and SkullSatamon and becomes SuperDarkKnightmon he then opens a portal and goes through it. Ian loads all his Digimon and tells Ryo that they'll tail DarkKnightmon. Ian and his army run into the portal and wind up at the Nazi concentration camp.
(Numbers indicate order of appearance. Bolded characters are fought by the protagonists, and italicized characters appear only as a voice or silhouette.)