The new morde CC build has come! Check it out and give your input:
http://www.mobafire.com/league-of-legends/build/cc-tank-morde-conditional-72999

Build change:
I changed warmogs to frozen mallet (side note, if you are willing to sacrifice 200 MORE health and find yourself not getting anything out of frozen mallet's slow, grab rylai's.

pros:
- can permaslow people
- less downvotes

cons:
- lose 600 health
- lose good amount of hp regen (about 50)

If you are serious about mordekaiser and are open to what you may not think may work (i actually made this guide by putting together two items i personally thought sucked: Frozen heart + warmogs, and then built around them. The final product was better than all of the previous morde builds i'd tried and i tried a LOT) then read on.

The warmogs vs frozen mallet choice is yours. I'll choose warmogs MOST of the time.

Times for frozen mallet: when your team has a hard (off)tank (like olaf or shen) and little CC (like olaf).

Times for warmogs: if you don't have some inner abhorrence for it, most of the time (if not all of the time). The explanation is in "Items: why this and not that."

About me: I do not troll on alts. My name in game is The Attila. My ranking solo queue ranked is 1385. I've played 11 ranked games as mordekaiser (started fairly recently). I won 8/11 of them and my kdr in ranked is over 2:1 and assists are through the roof. Look me up.

This guide directs you to being a tanky dps. You will be unstoppable, and hit hard. He is not truly pure tank for the simple reason that mordekaiser has no CC. There are other full tank mordekaiser guides that revolve around disruption and inhibition. I will include a link to one in the not so distant future.

- first you want to mid
- position yourself to E their minions and them at the same time
- if you are against a ranged hard hitter (mf/trist) you want to e the minions to get shield then e them through minions
- at level six you should be able to E harass them until you can ignite + ult for the kill

If you lane
- you want to last hit as much as possible and only use your E often if they push.
- push only if you know it is okay
- wait for teamfights

Mordekaiser's motto is: "if you're dying, hit harder."
Your job in the teamfight is to fit as many of the enemies as you can into your E and hit them all.
Different from other champions, you don't want to just massively spam your moves.
Q and W can be used as fast as you want (w has a fairly long cd) your E, however, is much more important.
Use your E when your shield is down to recharge it. If you Q and W have gotten you a big shield (or a previous E) just run around hitting with your Q and W or auto attacking until your shield needs to be recharged. If you do not do this, you may E when your shield is already full (not get maximum efficiency out of it) then they all nuke you. Now you have no shield and you wish your E was up. (this style is more advanced play so know how to play mordekaiser first.)
Your main goal in the teamfight is to get in people's faces (mainly the squishies), hit everyone with your W and E. And KEEP YOUR SHIELD UP.
If your teammates are still in the fight THEN YOU BETTER BE.
The most important role you have in the teamfight is ULTING THE RANGED CARRY RIGHT BEFORE THEY DIE. You want to make sure your ult will kill them (only getting used to morde can grant you the experience you need to know when). Once you have your ranged carry (or atk speed melee carry if they don't have a ranged carry) you can now win the fight all on your own almost REGARDLESS OF YOUR HEALTH. Reasons why:
Your ghost, per auto attack, replinishes 30% your shield for 30% of the damage it does (even if the damage is done to a tower), combine that with your skills and you have a never ending shield.
Also realize that your shield functions a lot like an extra health bar,it benefits from armor and magic resistance.

At the point where you have their carry, proceed to kill the whole team in order of importance. It WILL be easy.

NOTE: you do not have any CC. If you think it is ultra important, pick up redbuff (but not b4 your own dpser). However, mordekaiser is all about the teamfight, he can be 0/9 and still come out on top with a teamfight. He doesn't need any cc because he is all about winning teamfights, not chasing enemies 1v1 through jungles. If they run, you eat their towers because you are the strong pusher that is mordekaiser.

I've spent countless games playing as mordekaiser. I've tried tons and tons of builds in many different variations (given i haven't tried physical dps mordekaiser) and I have determined this is the greatest build and i'll explain why.

It is the only combination of items that gives you EVERYTHING you need against ANY good team comp.
The build:
- achieves 200+ mag res
- achieves 200+ armor
- achieves 3k+ health
(this fulfills all your tank requirements
- achieves an aura of 20 mag res reduction
- achieves personal mag pen of 52 + 15% (with runes and masteries)
- achieves AP of 292
- reduces your cooldowns by 20% (only inclusive of items)
- has an aura that slows dpsers attack speeds by 20% CONSTANTLY (better than randuin's 35% for a limited time)
- approx. 100 health regen per 5

Why are these important?
1) you have excellent tank stats
2) this is synergized by your shield that feeds from your ghost (granted by your ult) and your ap+mag pen
3) although some people think you are ignorable, you will be in their faces with aoe damage and slowing their attack speeds by 20%.

Masteries:
- You want the 9 in offense because the 15% spell pen is invaluable to you.
- You want 21 in defense because the extra resistance combined with 4% damage reduction synergize with your shield.

Runes:
- You want magic resistance per level glyphs because it helps you break 200.
- You want armor resistance per level seals because it helps you break 200.
- Magic pen marks because magic penetration is invaluable to you.
- 1 Movespeed quint to make you reach that magical 420 movespeed.
- 2 Magic pen quints because you rock with magic pen.

1st off the seemingly questionable one: Frozen Heart. Why would we get this?
- wasted money on mana? Perhaps, but the rest of the bundle is just too efficient.
- well first off the build needs armor
- the build needs cd
(mordekaiser can also take lots of punishment so auras are good on him: hence abyssal and frozen)

You might think, why not get thornmail?
- simply put: thornmail requires them to hit you to yield benefits
The cd on frozen does not require them to hit you for you to put out more damage.
The reduced attack speed aura does not require them to hit you.

Why not sunfire?
- not enough armor
- ample health is in other parts of the build
- not enough damage from the sunfire
A tanky dps opponent with 125 mag res will take 55.6% reduced damage from the sunfire dropping it to approx 18 damage per second. This is the equivalent of minion hits. You W already does good damage with pen and AP. If you are going against an even tankier person with 150 mag res, your W will do 74 damage per second to them.

But... But... Guardians?
- not enough armor (close yes)
- mordekaiser won't die until the rest of his team has LOST the teamfight. At this point, reviving won't do you much good. Unless your enemy has focused you, in which case they should lose for focusing the tank anyway. (however, look back at the teamfight section, you should be able to survive anyway).
- Still doesn't yield benefits if they don't attack you!

Why warmogs?
- You need to break 3000 health to be an efficient tank. (simple rule is 200 arm, 200 magres, 3k health)
- Getting an item that gives 1370 health (to a good farmer like mordekaiser) lessens the pressure on other items because they won't need to yield as much health (if any).
- Added bonus, it makes force of nature heal you for more.

Why Force of nature? And why so fast?
- your moves cost health, therefore, you don't want to committ suicide so early on you should get 2 regrowths (the amount required to cancel out your costs).
- in the lane, harass generally comes in the form of an ability which generally comes in the form of magic damage. So you want a negatron early.
It just so happens that those things build into force of nature which give you 7% movespeed! Enough to compete!
- Gives tons of magic resist (most per any 1 item)
- Synergizes with Warmogs

Why abyssal?
shouldn't ask this question... but for kicks
- gives AP
- gives magic pen which is more valuable (flat is better b/c it helps you eat the carries) and this is great on you b/c your moves don't scale well with AP.

Why Sorc boots?
- pen is good.
- Mercs, no real need for them, you have the mag res and you probably won't be targeted, and if you are, good for your team, you can take it.
- boots of swiftness, it's not necessary especially when you can't slow them with it.
- CDR boots are a reasonable argument here. Here are the numbers (based on a teamfight lasting 15 seconds)

These numbers are based on my full build lvl 18:

Pen boots (rounded)
Q: will be casted 4.7 times
W: will be casted 1.6 times
E: will be casted 3.1 times

First off Q (in a 15 second teamfight, per person hit) will do (rounded down):
vs225 magres: 592 dmg
vs150 magres: 799 dmg
vs100 magres: 1052 dmg
vs75 magres: 1245 dmg
W will do (this is calculated by saying you use it as the fight starts, nothing with cooldown and then using it for the remainder of the 15 seconds)
vs225: 605
vs150: 814
vs100: 1067
vs75: 1265
E will do (per person hit):
vs225: 496
vs150: 669
vs100: 880
vs75: 1041

With the cdr boots
Q: will be casted 6.25 times
W: will be casted 2.1
E: will be casted 4.1 times

Q will do:
vs225: 750
vs150: 987
vs100: 1243
vs 75: 1437

W will do:
vs225: 676
vs150: 897
vs100: 1118
vs75: 1300

E will do:
vs225: 623
vs150: 820
vs100: 1033
vs75: 1197

As you can see, cdr boots in theory will do more damage in a teamfight
given you are uninterrupted by a stun. You may think these are contradictory to what I told you about teamfights, given that most of the time we won't be spamming our E unless our team really needs the dps or our shield is massively being eroded. And you would be right. They are conditional.
CDR boots vs Mag pen boots are a matter of preference and amount of enemy stuns.
more stuns = mag pen
less stuns need more dps = cdr
Also, end game = sorc pen boots b/c blue elixir gives 10% cdr. Nullifying half of the cdr boots.
It all DEPENDS. It seems impossible to test, but I've given you the numbers to make your decision, as you can see, mine was mag pen boots.

Ult numbers are not included b/c ult should be used as a last hit on carries.*

Why rab cap?
- don't ask this
- gives most ap in game (particularly for non mana user)
- it compliments the amount of spell pen
- makes you do real damage