This is Just a quick intro to Playing Mordekaiser in mid elo games. You already have to understand the basics of Mordekaiser to Really maximize this playstyle. He is not for everyone, so don't call this build bad because this will work 90% of the time against decent, but not great teams. you also have to understand a decent bit of concepts to maximize his potential so if you come here saying: "yea, I kept using siphon on the minions like you said to keep my shield up, but they would keep ganking me. this is a noob build it doesn't work!!11!!!1" then I know you weren't really reading it carefully and I'll show you where I said otherwise. Mordekaiser can be shut down easily, so just because you are decently tanky does not mean you're invinicible; you will go down if they want you dead. Morde Requires a strong carry on your team, A tank with hard CC, perhaps tanky dps or caster, and a support. make sure you have at least 3 hard, dependable CC otherwise This will not work.

no. Just no. there are many reasons why mordekaiser should go AP rather than tank. one reason is because of the scaling on most, if not all his abilities is extremely good, around a .6 average for his basic 3 skills and a .05 scaling I believe on the ult. This doesn't sound like much, but I'll explain later why it's good. also, he has no natural cc (crowd control) to use, so besides being tanky... he's really not a tank. Also with his passive he can effectively be a decent off-tank with the constant shield.

I like 9-0-21 because it gives me the CDs on all my spells and summoner spells, some health, buff duration(for baron and Blue for more CD) and gives me movespeed. my runes are such that I don't have to buy much regen so I can keep spamming in lane(although not too much). you might ask WHY NOT ABILITY POWER QUINTS AND GLYPHS? THAT WOULD GIVE ME 20 starting ability power. thats way more than 5 more magic pen and 10% CD. I'll tell you why right now; cooldowns allow you to use your spells much more, making up for that AP scaling. sure 20 AP sounds like a lot, but thats 435 gold. whereas there are only 3 magic pen items, only 2 of which are useful. with sorc shoes and magic pen marks and quints, gets you to 35 magic pen. then you can get a void staff and just troll them.

Pros of this Build:
1. LOTS of damage
2. you're pretty damn tanky
3. people will have to deal with you instead of your hard carry
Cons:
1. AP Morde really needs a solo lane, possibly taking it from a carry.
2. You're tanky, but vlad tanky; if they want you dead, you're dead.
3. there are harder AP carries in the game.

You want to farm as much as possible without pushing the lane. try to last hit, and use your e whenever they get close and try to harass you. if you have good wards and map control, you can aoe farm a bit but it's slightly risky. also, always take farm over kills. 1 kill= 20 CS. plus CS is a constant value, whilst killing is reduced everytime

Try to take a solo lane, preferably mid. Your not extremely mobile, so the short distance in mid slightly makes up for it. If you can't get a solo lane, then a Regeneration Pendant is a viable item, but be warned; you're extremely squishy. try not to use your Siphon of Destruction too much otherwise you'll push your lane a lot. instead, time it so that you get your shield as soon as they harass you. This limits their harass, doesn't push your lane as much, and you harass them. It's a win win!
At level 6 if you had been keeping up with harass, then they should be at about 400 or so health. keep harassing but at this level, only use your ult for 2 reasons:
1. if they are committed to the fight and you can win
2. You can't win the fight and pop a defensive ghost
Defensive ghost is when you use your ultimate as a defense, not an offensive move. At level 1, it does little damage, but the 10% or so of their health can keep you alive till you make it to your tower. you can also use it to scare them out of lane or to stay in lane a bit longer/

Like said before, you can get a Doran's Shield or a regeneration Pendant to start off with. for boots, I like Boots of Swiftness because I started playing him a looooong time ago when that was the norm. now i would get Sorcerer's Shoes or Boots of Lucidity. next get Rylais Crystal Scepter and a Rabadon's Deathcap.
now here's where you can mix it up a bit. for heavy AD teams, I recommend Randuins Randouin's Omen for CD and the passive ( reduces enemies attack speed) and Zhonya's Hourglass. if you want a lil' more defense then get any other armor item, these are just the ones that syngerize with morde the best. for castor's you can get FoN Force of Nature. this increases your movement speed and gives you a lot of regen. plus this gives you the best MR for a single item in the game making it a great item for anyone. another item that I don't like that much is Abyssal Scepter but gives you more damage but less resistances. however the aura is a bit like magic pen so that's a plus. get a void staff to wrap it up and your good to go.

In a team fight, you're main goal is to kill their squishy, whether AP or AD. your Ultimate does max health damage, allowing you to kill that malzahar with 2100 health but 40 Mr as easily as a 1600 health Ashe( well maybe a bit harder). since you do decent damage and you're in the front,you might get focused. don't worry, your passive Iron Man will keep you alive a bit longer as long as you keep spamming spells. You have no CC except the slow from Rylais, so keep that in mind when entering fights.

I WOULD NOT recommend playing morde in ranked. people who do play ranked and are decently good understand how to shut down Morde. unless you're the godliest morde, you're gunna get f**ked.