"Wei Wuxian is the first one I would go to for such a puzzle, too." It's not a puzzle that comes up often in his own life, admittedly. Claudius feels a mixed yet strong respect for Nie Huaisang (like certain drinks). Certainly, he'd preyed upon Mo Xuanyu in a moment of weakness ... but also gave him the means to take revenge¹. While bringing back a lost friend and ally on which Nie Huaisang could rely, sharply aware of what was possible on his own, and what was beyond his abilities. A useful skill for for a head-shaker to have.

¹ It's just something Claudius might considering doing if he had a vengeful young man in front of him and a problem to solve, that's all. Perhaps not the whole self-sacrificial ritual. (It's incidental that the duel at the end of Hamlet turned into a sort of self-sacrificial ritual for revenge.)