Demon slayer infinity castle

Demon slayer popcorn bucket & cup combo with a Mugen Train arc is Enmu, the Lower Rank One of the Twelve Kizuki, who inflicts a dream-inducing curse on passengers and the Demon Slayer Corps members on board the train. Enmu is an antagonist who fuses his own body with the train itself, making it a challenge to defeat him.

Who is Enmu?
Enmu is a demon belonging to the Twelve Kizuki, a group of the most powerful demons serving Muzan Kibutsuji.
He is the Lower Rank One, the highest-ranking demon among the Lower Ranks.
What is Enmu's goal?
His goal is to kill the passengers and demon slayers by trapping them in a dream-like state and making their bodies unable to wake up.
He tries to make humans fall into a deep slumber by manipulating their dreams.
How is Enmu defeated?
After falling asleep, Tanjiro, Zenitsu, and Inosuke must fight through the dream world to destroy Enmu's core and his connection to the train.
The trio eventually defeats him through a coordinated attack.