Descaling: Thundering Grief
I highly recommend using 2 hydro + 2 dendro characters. You may replace them with other characters with the same element composition or you may also use 2 pyro instead of dendro.
Remember to replace the Challenge detail, Opponents’ Pyro RES increase with Dendro RES increase. Just make sure 1 of them is a healer and you’ll be fine.
Piety: Calamity of Blazing Steel
I highly recommend using hydro, dendro & pyro characters with at least 1 archer & 1 healer. You may also use other characters with different elements but make sure to make some changes on the Challenge Details, Opponents’ element RES increase.
Pay attention to the glowing yellow light, immediately switch to an archer character and hit it with a charged attack.