Looks like Sanctus is putting the smack down on Arius. Though to be fair he does have some feats here and there. Here's what I've got, (bare with me as some of it may be a bit exaggerated)
Speed:
Arius doesn't really show much outside of dodging Dante's sword swing in one cut scene. Graphic wise it looks pretty pitiful but taking into count that this is the strongest Dante, it holds a little merit I guess.
He also has some darn good acrobatics as he flips around his table when you attempt to attack him. What I think should be noted thought, is that like Sanctus, Arius also has teleportation which he does frequently when battling him in and outside his office. He has one other technique that turns his body into dark matter that carries him around at a very quick pace. While like this he is insurmountable to all forms of damage in those moments.
Strength and abilities:
Arius carriers a demonic revolver when he battles. Considering that this is his only weapon, it must have trumendous fire power. Arius' main method of fighting is dark magic however and he has a pretty big arsenal if you take some things into account. Like Sanctus he can make a shield to protect himself, HOWEVER, unlike Sanctus' shield, it doesn't break when attacked too many times. While under his shield he is completely invulnerable until he decides to let it up again to attack. He also doesn't seem to have a waiting time or a limit to how many times he can use it.
>He can create large spikes made of pure energy and he can send them into the air or on the ground at will.
>He can create a tiny black hole anywhere near his opponent sucking them inside. While inside he compresses and crushes them before warping them into the air and dropping them.
>He can make a sort of dark matter grenade.
>He has the ability to summon a number of lesser demons like the Goat clan for air combat, a number of different Msira, Savage Golems and even pretty powerful demons like Furiataurus and most annoyingly, Secretaries (which have the combat speed of base Lucia and a butt load of health)
for ground combat.
>Apparently he molded most of those skyscraper sized buildings himself, with his magic. One even transforms into a full fledged demon (Nefasturris) who could fire lasers on the fly and likely destroy and entire city block with ease. Because Nefasturris is made up of thousands of Nefasvermis', Arius would have no trouble at all unleashing more than one if they fight in a large area.