Thread:BowserRulesAll/@comment-11564515-20171007204823/@comment-27109830-20171007205745

Kurapika VS Nico Robin has a description in the Thumbnail IIRC, as for Mayuri VS Caesar;

Both of them are pretty much the embodiment of the mad scientist stereotype within their respective series, who messed with their own demonic power source (which revolves around poisonous substances) by experimenting on it for a number of desirable effects, with Mayuri changing his Zanpakuto's Bankai and Shikai in a number of ways, and Caesar mixing his Devil Fruit powers with a number of chemicals. Both of them are incredibly intelligent and powerful scientists, but also sadistic to a fault, and ended up being forced to work with the heroes after their defeat. Also, both of them were voiced by Ryusei Nakao.