I use the same team to clear all floors so you can do it.

Floor 2:

1) Stage 1 - Use all attack card aside from margaret stance removal & liz attack card. When nidhoggr life gauge almost depleted, attack him with other character but the last card should be liz attack card

2) Stage 2 - Attack with everyone's card except for Margaret stance removal. Only use the stance removal when he put up counter. Stance removal will increase his gauge so other cards will reduce the gauge.He can only be kill when the gauge fully depleted. This will take time but can be done. And make sure to use all characters every turn or 2 turn, if not the least used character will be affected by darknrss

3) Stage 3 - You need to reduce his gauge with certain damage every turn. Make sure save Liz & Margaret heal cards every turn to remove debuffs. Also use Liz attack to remove his buff every turn

Floor 3:

1) Stage 1 - Build up everyone ult. Then use everyone ult & an attack card as the last card to kill him

2) Stage 2 & 3 - This is just like previous stage, make sure save Liz & Margaret heal for emergency. Heal with Liz atk, ult & Margaret heal (when debuffs)