post #1157771 shows a red oni with one horn, indeed, do a tag search and you can see a lot of red onis with one horn (and a lot of Chen for some reason)
Wasn't there a oni hierarchy of such where the amount of horns indicated rank?
No horns < one horn < two horns < two horns and three eyes?
Then again, you often see oni with two horns and one horn often paired, each beng as tough as the other. That, and Yuugi and Suika are sorta evenly matched according to SoPM (Suika's better at magic but weaker in strength, Yuugi's worse at magic but physically stronger).