The reason I asked you about counter attack is because M King is relatively slow.
Counter Attack Buff allows M King to take turns while being slow.
It is a very good Arena combo.
I like Rhazin + Seeker combo.
I run a similar team.
Based on what you have said, I would build Rhazin has nuker of team.
I would build M King as Shield Set / Immortal Set wearer.
I would probably use Scyl of Drakes instead of M Monster.
M King has highest HP in game.
I would play off that fact by using Shield set on him.
I am thinking of the following:
HP % Gloves
HP % Chest
HP % Shoes