Malum does not use mana. He instead uses his health to cast his abilities. Malum has 1 skill point invested into his ult at level 1.
As you can see, Malum's abilities are based on the seven deadly sins (DEFINITELY NOT OBVIOUS). His name is latin for evil, and the title was originally gonna be "Peccatum Originale" meaning "Original Sin", but I decided to change it because reasons. Have fun criticizing.