It finally worked out by one-shotting pallardo with Falling Star, warping Marianne, dancing, and doing it again. Keeping Byleth alive that long was definitely the biggest problem, as she couldn't stay in the initial 2x3, so I had to let her run along with the 3 fliers at the bottom, hanging on for dear life using nosferatu on enemy phase. It really felt like the scene in POTC where Jack desperately outruns a small army :)). If anyone else but Marianne had been my dancer, this would have been a whole other story xd