To accompany Ridley?! That would be tricky... Ridley is a more adult character, whom is also very much requested and has a back story that stretches into the entire Metroid series as whole... he's a genius, yet a monster...
If this end had to choose one to go with that, I would say Majora's Mask + Skull Kid. Dark, dark characters, not to mention tragic, mischevious, dominant... requested quite often from what this end has seen, too. Skull Kid in many entries of the Zelda series, but has only been Relevant with the mask through one, which may make things complicated, but that's okay. Another horrible monster, but this time concocted out of Corruption of an ultimate evil gone and found