Mordekaiser is a tank with a shield, a tank with lifesteal, and some more shield.

He has these abilities:

Q) Ace of Spades:
Damages 3 nearby enemies if there are nearby enemies, if there are none, hes does double damage to a single enemy.

W) Creeping Death:
A metal shard shield that is DPS while adding to armor.

E) Siphon of Destruction:
Does damage in a cone, and adds to your shield.

R) Children of the Grave:
Does DPS, but if you kill an enemy (your target), he becomes a slave to you, with massively increased health.

PASSIVE: Iron Man
Adds 20% of ability damage to shield, and drains 2% of shield per second.

Items:
Start with:
Dorans Shield
Heal Potion

Boots:
Berzerkers Greaves

Weapons:
Guinsoos Rageblade
Bloodthirster
Frozen Mallet/Infinity Edge

Other Items:
Phantom Dancer
Warmogs Armor/Force of Nature
Starks Fervor

Skills to get first:
Siphon of Destruction and Mace of Spades, get Creeping death @ lvl 4.

Runes:
I use attackspeed runes, because at the beginning of a game, you need it, for just about everything with Morde.
I also use armor, and i have attackspeed quint's, and cooldown reduc glyphs, for maximum ace of spades spam and siphon of destruction spam.

Summoner Abilities:
Exhaust/Heal
Cleanse


Mordekaiser is the ultimate meatshield, due to the fact his Shield blocks EVERYTHING.
Be sure to spam your abilities to get his Shield up before anything else.

Masteries:
•3 in Deadliness
•1 in cripple
•4 in Sorcery
•4 in Alacrity

•3 in Hardiness
•3 in Resistance
•2 in Evasion
•3 in Harden Skin
•2 in Defenseive Mastery
•1 in Willpower
•4 in Veterans Scars


With Guinsoos Rageblade, you are a tower killer, you NEED to push and feed your allies as soon as you can, or feed yourself, people dont like fighting Morde due to his shield, and his ultimate, because if he kills one, they both focus on the other.
The Bloodthirster will enhance your Guinsoos Rageblade intimately, making you kill towers in seconds.
The Dorans Shield at the start gives you a bonus to health and regen, so you can spam abilities, and your health can regen if you just tower hug.
Morde is a two versus one master, if he kills one, the other turns n one of them, and your damage output is doubled, as well as your attacks, so say you take out a Warwick with your COTG and are fighting a Ryze, your damage output (if hes a GOOD warwick) is now at least quadrupled, by the selection of the 1v1 master. You may now go LOLOLOLOLOL at the stupidity of the enemy running away, into the ganks and abuse of your allies.

I am currently developing a Tanker's guide to this as well. Will give the item list soon enough.

Please rate/comment/help out with this guide.
Still in work.

Bad. by the time you get your bloodthirster you wont need to kill turrets, and you sure wont take them down in seconds with mord.

Edit: Then again your name is "failboat".

Well, I'm sorry if this isnt efficient, seeing as this build ha worked for me and got me a winstreak, help is appreciated though, please, give me some advice on him, ive only been playing him one day.
Unlike the other guy who made a guide, T0ggle, I'd prefer this guide to be made from people who KNOW how to play Morde like a pro, these are only my assumptions from playing him and basically only him for a complete day.

Really? In my (admittedly low) experience, I've found the Rageblade to be pretty ****. Morde doesn't have very good attack speed, gets almost no benefit from AP items (below 100 AP for his ult), and spends more time positioning and casting than autoattacking. Guinsoo's just doesn't feel like a good fit to me.

Might I ask why you like Attack Speed runes so much? I'd think, considering the way that MoS works, you'd get better return out of stacking damage, even to the exclusion of Attack Speed?

Something else that I notice is that you are waiting really long to get anything resembling a survival item. If you are tanking, you should be purchasing items that let you tank longer. Morde's HP is actually on the low end of things (probably due to his shield), and waiting until you are 3000+ gold into a game to get any HP (other than Doran's Shield) seems weird to me.

I do like the Mastery setup. I'm getting tired of 21/9/0 or 9/21/0 only.

Ah, but the Rageblade is good for you creepind death and siphon, it adds a small amount of damage so you and start hurting towers better.
I have a lot of attackspeed runes because thats the build i use in my runebook, i dont ever change it since i completed it.
He doesnt need that many survival items because you have his 550 hp shield, which if your doing Mordekaiser right, will pretty much let you survive anything from a few hits from a turret to a twitch shooting you in the ass for a few seconds.
Please, i need more advice, someone else?