Marks are like the ones from the weekly boss (adjika, hijab... you get the idea). But yeah, it seems like they don't stack. The shield also helps a lot there, but you need a character that's not level 20 anymore.
I finally cleared level 11 with 9 stars for the first time. To defeat the third room, I had to take Hu Tao in the first half and endure a huge cooldown on her skill, so that I could quickly defeat the enemies in one stance. The second half with Goat + Diona passes more or less easily.

В тихой однообразной жизни всегда так бывает: каждый отдельный день бесконечно долог, но месяцы и годы мчатся с непостижимой быстротой.
I wanted to offer you some flowers, but a crown would suit a princess like you much better
Смысл жизни в том, что жизнь на тебе не заканчивается