Kai VS. Zuko is generic (plus Kai would win mid-dif) I want a match-up where there isn't quite an obvious winner, so.... Kai VS. Azula (Rules in Description) : r/Ninjago
LEGO part 76923pb02 - Bright Green Dragon Head (Ninjago) Jaw with Large Spike and 2 Bar Handles on Back with Yellow Eyes, Dark Green Scales, and White Teeth Pattern at BrickScout