This is just my take on how I play Morde. You kill by out lasting everyone not out dpsing them. I dont stack health because you really dont need to with Morde, his shield is 600 health that can be restored in a couple of seconds. I think that having 6k health and getting crit for 500 or more is kind of pointless bc it is only going to take 10 to 12 hits to kill you. When u stack armor and MR, with 3500 health and only get crit for 85 to 100 it makes a difference. The real key to Morde is to keep your shield charged, stay in the minions. He is an awsome lane pusher and once you kill someone and steal their soul multi kills come easy as well as downing towers.
Ghost: Mordes biggest weakness is that he really doesnt have a good way to escape. Ghost provides that as well as the ability to chase early in the game since he also isnt the fastest champ in the game. But what do u expect from a guy wearing armor?
Ignite: The ignite + Children of the Grave combo is old news but it does work, get them down to quarter or less health blow both Ignite and CotG and get yourself a soul.
Pretty straight forward, you are trying to take as little damage as possible.
I always use flat runes instead of per level runes. To me early game is far more important than late game. Come out of the gate and smash face early and get the leveling and item edge.
Mark of Insight: All of Mordes abilities are AP based so the magic pen helps his damage a little.
Seal of Potency: Ability power or dodge runes, which ever you prefer. I am cheap so i went AP runes. I never seem to have a problem surviving anyway so i dont see a need for the extra dodge.
Glyph of Focus: Pretty much explains itself, lets you use Mordes minion wave clearing abilities that much more often.
Quints of Fort: Since i dont stack health I thought I would get a little extra in there someplace.
Iron Man: It is your shield, your main survival tool. Its like having 600 throw away health. 25% of all the damage you do is converted into the shield.
Mace of Spades: On your next hit you hit 4 targets, your main target and 3 random other targets. If the target is alone that bonus damage is doubled. This your main ability against champions and also your secondary minion wave clearing ability. The fairly short Cd lets you use it often.
Creeping Death: Deals aoe damage for 6 seconds and the damage is modified by your AP. There are two things about this ability that most people over look, it also raises your armor and MR, and you can cast it on any friendly target. Is your lane partner in a tight spot and trying to escape? Toss Creeping Death on them, the extra armor and MR could save them, and the aoe damage my scare away the chaser. Steal a soul? Put Creeping Death on the soul and send it after other players or have it tank a turret. Easily 75% of the time though you will put it on yourself for the extra damage.
Siphon of Destruction: This is your main shield charging ability and minion killer. If you aim it right you can hit all the minions in a wave with it. Its damage is also modified by your AP. This is your first ability, it has a slightly longer range than you would think.
Children of the Grave: This is Mordes ultimate, you steal a percentage of there life over 8 seconds and it heals you. The amount of health you steal increases with your AP. If your target dies with this is active you steal their soul for 30 seconds. Morde gains increased AP and AD while this is active and the soul gains part of Mordes adjusted stats. This turns you into a power house making multi kills rather easy. Toss CotG and ignite on your target to really melt the health away. This can also be used as an escape tool, healing you and sometimes scaring your attacker off. The only thing is cleanse removes it, so watch for champs that use it.
My core items are Randuin's Omen. Mercury Treads, Guardian Angel, and Rylai's Crystal Scepter. The last four items can be swapped in and out depending on the team you find yourself against.
Heart of Gold: I build this first, its part of Randuin's, gives you health, armor, and some gold gen.
Mercury Treads: Since Morde doesnt have an escape ability this are a must for getting away. 25% shorter stuns, slows, blinds, taunts, and whatever else you dont want on you is great. The MR also gets us headed in the right direction.
Guardian Angel: 68 armor and 38 MR, plus the passive revive every 5 minutes. With this build you shouldnt have to use the passive much but it is nice to have, it really makes the other team hate you.
Warden's Mail: 60 armor,25 hp/5, and a 20% chance on being hit to slow your attackers run and attack speed by 35% for 3% seconds. How do u like that Yi, Warwick, and Xin?
Randuin's Omen: 90 armor, 300 health, 25 hp/5, 15% CD reduction, same 20% chance to reduce attackers run and attack speed by 35% for 3 seconds. And you can activate it to reduce surrounding units speed by 35% for 2 seconds, this time is extended by a half second for every 100 armor and MR that you have.
Rylai's Crystal Scepter: 80 Ap, 500 Health, and abilities slow enemy movement speed by 35%, 15% for multi target abilities. Ok some people my ask why Rylai's over Frost Mallet? Morde is not an auto attack champion, most of his damage comes from his abilites. The slow of course helps with chasing people down, not only for you but your team mates. Even though its only 80 AP it does give your abilites a small boost in damage and this makes your shield charge slightly faster.
The last four items can be switched around depending on the other teams make up, you may be finding yourself to need more armor or more MR, or take one of each if it is a split team.
Banshee's Veil: 450 health, 400 mana, 57 MR and a passive bubble that eats the first enemy ability that is cast on you, this has a 30 second cool down. Yes that mana is wasted on Morde but you will be happy when the bubble eats Ryze's rune prison.
Force of Nature: 40 hp/5, 76 MR, 8 movement speed, and a passive that restores .35% of your health every second. The 8 movement speed is really nice since Morde is kind of a slow champion, this really helps with chasing down or getting out of a sticky situation. Of course you should be the one making it a sticky situation. And who can argue with that much health regen?
Thornmail: 100 armor, and when you are hit with standard attacks it returns 30% of the damage as magic damage. Just watch Yi, Warwick, Xin, and Twisted Fate eat themselves.
Sunfire Cape: 45 armor, 450 health and a passive that deals 40 magic damage to nearby enemies each second. Simple get in the thick of things, use your aoe abilites and watch people melt.
This is my first posted build, so im sure there are a few mistakes in here. This is just my take on the champion Mordekaiser and I usually do reasonably well with it, as good as 20/4/4 in 5s. Im not going to say that this build will make you superman because I have had bad games with it as well, it just happens. A few things i have noticed that once you get around 70-75% damage reduction either in armor or MR it begins to take alot more to increase the stat, so you may want to focus on more health or AP at that point. It is super important that you head into a team fight with your shield charged, its just that extra buffer. One thing I havent figured out about the shield is if your armor and MR reduction are applied to the damage it absorbs.