Oh skasio long time not seeing you.
Are you grinding in FGO?

And yea they consider as boss.

About the Use 1 or 2 team to knock Nidhogg down vid.
I think you can easy search in in Niconico or youtube.
But if asking that it's possible to do?
I may say I don't know.

In Nidhogg battle my friend use 2 team, first is debuff+boss killer team, second is solar drive team.
Yamabuki, Ivy, Yadorigi is in first team (not remember other 2 member).
Enichida, Manryu, Mimosa in secon team (again not remember other 2 member).
And 1 additional unit to help boost skill rate rainbow Lantana.