Muzan is old fashioned, being able to play piano, violin and flute, he also enjoys horseriding and is fluent in 70 languages
He loves experimenting and uses other demons for experiments, he once blew up his lab if not twice, 
He always wears gloves, not wanting to get dirty
Speaks Japanese, Russian and British, he lived in Russia for 50 years and then in England for 70 to learn the languages, probably talks rude things of demon slayers in russian or with a british accent
Has a fear of touched