Remember class cthulu is NOT a toy.

The point of that combination is how badly it works. It might be good as a reason for issues in the storygame sorta like how the great lich lord is the reason for the bans that are a plot point in necromancer. As far as I know you can't have a demon as your teacher in necromancer, big red gets killed and vilvex has demons kill you if he is freed.

Sorcerer/Distorter would allow for teleportation distortion, make a fortune in the transportation business, teleport brains into the sun etc.

Distorter/Evoker would allow for creation distortion such as creating a large amount of non-magical fire/water/diamond/minions etc. This could be used for stuff like fireballs and dropping rocks on people (rocks fall everybody dies anyone?) or making loyal minions or valuable substances.

Necromancer/demonologist allows for demons and undead or undead demons.

Necromancer/evoker could raise undead and equip them with weapons made by the evoker element.

Chaos master/Demonologist could allow for some weirdness, make a nice enemy or protagonist, if protagonist then you have the issue of their magic's inherent destructiveness if villain they can make huge messes for the protagonist to clean up+have some strange abilities and motivation. This one is good for general weirdness.