Mammon is the second oldest and known as the Avatar of Greed. True to his title of 'Avatar of Greed', Mammon is naturally greedy and always seeking out opportunities to profit without putting much work. Although he's the second eldest, he acts immaturely when he doesn't get his way and is the biggest troublemaker of the brothers. He's egotistic and prideful, though it seems that it is only a façade to cover up his soft nature. He often refers to himself as "Ore-sama" and "Mammon-sama". "-sama" is a Japanese honorific given to people worthy of the utmost respect, so Ore (crude pronoun for me, I) -sama is, essentially, "The Great Me". Mammon is also quick to lie, but not very good at it; in many stories and chats, he stutters when he denies something (even while texting). He has a tendency to shout whenever he's angry or upset (which is most of the time) as well as growl when he's irritated. He often praises himself when he thinks any of the brothers compliments him (even if they aren't) and thrives on being complimented, especially by mc. espite his rashness, Mammon is sensitive to changes and highly empathetic; he's the first to notice if something is amiss with his brothers or MC. 

For reference to what I'm looking for in terms of voices, he is a clip of the Japanese voice actor: https://www.youtube.com/watch?v=6SQ94BsrNyU

(My opinion) It's a medium range of voice. Needing someone who is both very energetic in how they talk, but also able to flip around emotions with ease. A unique characteristic to the voice (not cartoonish though) would also help you stand out- wether that is a slight raspiness to the voice or something that makes the voice sound unique would help you stand out for this character. 

Anything in () is suggestions or context clue. all caps are words that have emphasis.