Kokushibo states that slayers die at the age of 25 due to the curse.

Kokushibo reveals this when he meets Muichiro

What age do marked slayers die at?

Selfless State made Tanjiro appear like a tree to Akaza

Giyuu and Sanemi were the only two surviving Hashira

Yoriichi died of old age while standing up

Sun Breathing was the progenitor of all Breathing Styles

Muzan split himself into 1800, and Yoriichi cut 1500

His wife and unborn child were killed by a demon

He wanted to get revenge against his father

Ubume, Lower Moon 1 was said to create illusions so powerful  you  could not tell reality from illusion.

There are 14. Insect, Wind, Love, Thunder, Flame, Flower, Water, Stone, Moon, Sound, Beast, Serpent, Mist, Sun

Jigoro killed himself after learning Kaigaku became a demon, letting the teachings of Thunder Breathing fall to the demons.

Muzan was killed via a combination of Shinobu's Poison and Tamayo's anti-aging posion, in tandem with the rising sun and the hashira.

Biokinesis; Muzan can control his cells at will, allowing him to manipulate both his blood and his body.

Hinokami Kagura is Tanjiro's adaptation of Sun Breathing. While he did use Thunder to catch up to Hantengu, he did not use it combatively. 

This quiz includes spoilers from the manga, so be warned. 

These questions were made to be obscure! Don't be let down if you can't answer some.