Yeah, youtube isn't really the best place to look up dmm games gameplay unfortunately. However, there should be plenty of videos on each nidhogg event on nico.
Although if you did search it up in japanese instead, there should be a few video would showed up, like this one from HydroKirby for example.
youtube.com/watch?v=9GUJGMALdj4
Although you can probably just 1 shot every phrase with 1 party in all difficulties if u wanted, like using RR/Yarrow/Cowslip/Colchicum/Kugaisou.