Quote Originally Posted by Unregistered View Post
In addition, the wiki page for light Tsukuyomi points out that the element resist debuff also reduces resistance against debuffs from that specific element. So light resist debuff functions both as light-specific def down and a debuff resist down effect for light-only.
So if you don't already have a normal debuff resist debuff, you use the element resist debuff first, then try to throw your other debuffs (from kamihime of the same element).
That's interesting, but one of the features of Mordred's debuff resistance down ability is that it rarely misses. The same probably can't be said for Tsukuyomi's ability. For my Water team, if debuff resistance down misses, I'll often get multiple misses of other debuffs, and that can easily cause a wipe in difficult content like Accessory Quests Rank 4.