Mordekaiser is a great 1v1, 1v2 champ and even solid mid character.

Many people have a misconception of Mordekaiser. They label him as a tank and dismiss all other comments on the matter. Let us consider what a Tank does. A tank needs to be able to absorb damage, and refocus attacks off his dps onto himself.
Absorb Damage (check)
Taunt or incapacitate attacker (left blank)

Since we have no method to pull people off of our dps (like Rammus, Shen, Galio..ect) then we cant really be called a tank. Basically we would be dancing in front of the enemy line saying "Hit me, not him. Hit me!" That would be useless. We therefore determine that Mordekaiser is a very thick AOE mage. You say "Wait a minute! You tricked us!" Really? Every single ability on Mordekaiser is area of effect (except his ultimate). Mordekaiser does not even come with a built in slow or any method to control the movement or attacks of the other players. For that reason, I believe we need Rylai's Crystal Scepter and Frozen Mallet.
You say, "Wait i think i see a pattern to your build." hmmm go figure. I am a AOE mage that must be in base contact. I believe i have to be thick for that to work. Okay, I basically grab all the Giant's Belt items i can get a hold of.