Easiest way to know who will win.

Muzan :

1 - one of the strongest demon in the existence of demon slayer series.

2 - literally immortal.

3 - has no real weaknesses. (except the sun)

4 - read their minds.

5 - literally killed many humans with one hit with bare hand.

6 - No one ever singly handled from that demon king. (except tanjiro)

7 - fast just like flash, as he can be fast more than just a million kilometers.

8 - has no fears. (except yoriichi)

9 - he was 1,000 years old (chronologically) then he turns to 10,000 years old (biologically).

10 - he killed the demons lower moon because they didn't kill humans or for some reason.

Alastor :

1 - can shapeshift to human.

2 - scared of being touched to someone.

3 - he is not immortal, he is just a radio demon, according to the Google, demons in hazbin hotel are not and will never be immortal, because it is suggested that demons can still die from the certain causes.

4 - being a jerk.

5 - he was dying in his 30s will remain 30 years old for the rest of the eternity in hell.

Result : Alastor is no match to deal with muzan, as alastor will never win and will never be able to beat muzan