Mordekaiser recently go buffed with the release of shield bash. He is currently sitting at a 52% winrate.
Have fun.

Passive Iron Man
Mordekaiser shields himself for 25% of the damage dealt from abilities, absorbing incoming damage (shield generation is only half as effective against minions).

The maximum shield strength is equal to 25% of Mordekaiser's maximum Health, while the shield decays by 1.5% of his base Health every second. Once the shield reaches 25% of its maximum value, it no longer decays.

Q: Mace of Spades
Mordekaiser's next 3 basic attacks are empowered. The first and second attack deal 10 / 20 / 30 / 40 / 50 (+0.5 / 0.6 / 0.7 / 0.8 / 0.9 per attack damage) (+60% of ability power) bonus magic damage, while the third attack deals double that amount at 20 / 40 / 60 / 80 / 100 (+1.0 / 1.2 / 1.4 / 1.6 / 1.8 per attack damage) (+120% of ability power) bonus magic damage.

Cooldown: 10 / 8.5 / 7 / 5.5 / 4

Cost: 20 / 23 / 26 / 29 / 32 health

1st and 2nd Damage: 10 / 20 / 30 / 40 / 50 (+ 50 / 60 / 70 / 80 / 90% AD) (+ 60% AP)

3rd damage: 20 / 40 / 60 / 80 / 100 (+ 100 / 120 / 140 / 160 / 180% AD) (+ 120% AP)

total damage: 40 / 80 / 120 / 160 / 200 (+ 200 / 240 / 280 / 320 / 360% AD) (+ 240% AP)

W: Harvesters of Sorrow
Passive: If Mordekaiser shares experience with an ally, his experience penalty for sharing a kill is only 50% of what it would normally be.

Active: Mordekaiser targets an allied minion, champion or himself. For the next 4 seconds, Mordekaiser and the target allied champion gain 75 bonus movement speed when moving towards each other. When near enough to each other, they also each deal 35 / 45 / 55 / 65 / 75 (+22.5% of ability power) magic damage per second to nearby enemies for the duration.

At the end of Harvesters of Sorrow's duration (or when Mordekaiser reactivates it), he deals 50 / 85 / 120 / 155 / 190 (+30% of ability power) magic damage to all nearby enemies and heals both himself and his ally from up to 2 targets hit for the same amount (healing is reduced to 25% against minions).

Range: 1000

Cooldown: 12 / 11 / 10 / 9 / 8

Cost: 25 / 35 / 45 / 55 / 65 health

MAGIC DAMAGE PER SECOND: 35 / 45 / 55 / 65 / 75 (+ 22.5% AP)

TOTAL MAGIC DAMAGE: 140 / 180 / 220 / 260 / 300 (+ 90% AP)

HARVEST DAMAGE: 50 / 85 / 120 / 155 / 190 (+ 30% AP)

HEAL PER ENEMY: 50 / 85 / 120 / 155 / 190 (+ 30% AP)

MAXIMUM HEAL: 100 / 170 / 240 / 310 / 380 (+ 60% AP)

HEAL FROM MINIONS: 12.5 / 21.25 / 30 / 38.75 / 47.5 (+ 7.5% AP)

MAXIMUM HEAL FROM MINIONS: 25 / 42.5 / 60 / 77.5 / 95 (+ 15% AP)

E: Siphon of Destruction
Mordekaiser damages enemies in a cone in front of him, dealing 35 / 65 / 95 / 125 / 155 (+0.6 per attack damage) (+60% of ability power) magic damage.

For each champion hit, Siphon of Destruction also generates 15 / 17.5 / 20 / 22.5 / 25% of Iron Man's maximum shield

Range: 700

Cooldown: 6 / 5.75 / 5.5 / 5.25 / 5

Cost: 24 / 36 / 48 / 60 / 72 health

MAGIC DAMAGE: 35 / 65 / 95 / 125 / 155 (+ 60% AD) (+ 60% AP)

BONUS SHIELD: 15 / 17.5 / 20 / 22.5 / 25%

Ultimate: Children of the Grave
Passive: Mordekaiser's basic attacks and abilities curse the Dragon for 10 seconds. If Mordekaiser's team slays it, the Dragon's soul is enslaved and follows him around. Enslaving the Dragon disables Children of the Grave while it remains active and kills Mordekaiser's current ghost.

Active: Mordekaiser curses an enemy, dealing an initial 6.25 / 7.5 / 8.75% (+1% per 100 ability power) of the target's maximum Health as magic damage. For the next 10 seconds, an additional 1.875 / 2.25 / 2.625% (+0.3% per 100 ability power) of the target's maximum Health is dealt to the target as magic damage every second.

If the target dies while under the effect of the curse, their soul is enslaved and will follow Mordekaiser for 30 seconds. During this time, Mordekaiser gains 25% of their bonus Health and 30% of their Ability Power. Meanwhile, the spirit gains Mordekaiser's bonus attack damage and 15% of Mordekaiser's maximum Health.

Pets can be controlled by holding the alt key and using the right mouse button

Range: 650

Cooldown: 120 / 105 / 90

NITIAL MAGIC DAMAGE: 6.25 / 7.5 / 8.75% (+ 1% per 100 AP) of target's maximum health

MAGIC DAMAGE PER SECOND: 1.88 / 2.25 / 2.63% (+ 0.3% per 100 AP) of target's maximum
health

TOTAL MAGIC DAMAGE: 25 / 30 / 35% (+ 4% per 100 AP) of target's maximum health

GHOST DURATION: 45 / 60 / 75

BONUS Dragon ATTACK RANGE: 0 / 75 / 150

BONUS Dragon MOVEMENT SPEED: -50 / 0 / 50

Passive:
This is your main source of Tankieness, as the shields can get pretty big. Keep in mind that the shield only part of the way makes up for the Hp costs on his abilities. You will lose in the long run is you try to poke. All in's are Mordekaisers strength due to his shields and hp costs

Q:
This is your main damage source, there is not much else to this ability, other than it scales really well with the 3rd strike. This is basically what it looks like, more DPS on your autoattacks. I Max this ability second, or third if you want to Max E first

W:
The DOT Zone isn't too massive, but the recast is what really makes this ability good. The recast deals a good chunk of damage and heals you for a massive amount. This is a massive help in teamfights, as it will allow you to negate a round of abilities. I max this ability first always

E:
Damage and shield. Not much else to say. It slows if you have a Rylai's Crystal Scepter it slows. I max it second or third

Ultimate: Children of the Grave
This is probably one of the more powerful ultimate's in the game. A ult + ignite combo will be a death sentence for anyone under 40% health. The ghost is pretty good, as you can use it to win teamfights and siege towers. The Dragon is insanely good as well. I Level this whenever i can.