This is my first guide, and it is well subject to flaming(usually by noobs who won't even try the build).

First thing: AP Mordekaiser is the most common dps build. Because it is easysauce. Aim the cone, get shield, throw creeping death, maybe a mace of spades...

Whereas with an AD Mordekaiser, everything revolves around his Mace of Spades. This is his ONLY AD scaling ability. First you think "wow this is dumb, why would you build AD?" First, it scales 100% of your bonus AD. Second, the damage is increased by 70% if you've found an enemy champion that's all alone. Third, AP utilizes Siphon(in conjunct. with many enemies) to build shield, whereas Mace of Spades can build a full shield from one minion.

AD is a harder route to take because Morde has no CC, and no dash component, and many people see that as his downfall. However HE DOES NOT NEED ONE.

I expect that to get plenty of "lul your such a noob i would focus you down before you get to me."

No you wouldn't. I engage if it is JUST you or in a teamfight.
Terms:
MoS MAce of Spades
SoD: Siphon of Destruction
CoG: Children of the Grave
Win: What you do when you use this build.

Pros:

Fun
Different
High burst damage
Great chasing ability
Survivability through high damage output
easily destroys ap mordekaiser


Cons:

Difficult to master
weaker ult
less survivable than a tank build
more melee oriented
you get flamed if you are worse than ap morde

This is simple.
Greater Mark of Magic Penetration - Most of your damage is magic.

Greater Quintessence of Magic Penetration and/or Greater Quintessence of Movement Speed - You can build either 1 MP Quint and 2 MS quints; or 3 MS quints - The extra MS is important, you have to GET to your target to kill them.

Greater Seal of Armor - Armor and MR are calculated in your shield, and well, AD carries are annoying.

Greater Glyph of Cooldown Reduction - CDR for your mace. Duh.

Masteries: 9/0/21

Offense: Build the AP, because yes, AP falls into this build, but only to boost your AP abilities. Not to mention the crit chance is almost unnoticeable. Take CDR, it is very necessary to spam MoS. Magic Pen - Discussed in Runes.

Utility: Take Ghost, Good Hands (everything else is mana related, gross.), XP(Duh), Greed(you have nothing else to put that point in), Utility Mastery, Quickness(discussed in the runes page), Intelligence(yumm CDR) and Presence of the Master (CDR on my Ghost and Ignite? GG).


Summoner Spells:

Ghost: This is core for Mordekaiser. You have to GET to the champion to deal damage, take advantage.

Ignite: I usually take ignite for the purpose of a double dot on enemies. It can give you that final push for the kill in addition to CoG. That and it is mundo-bane.

Flash: This spell can be used for getting close to the target, or an escape mechanic. Just remember, the more you use flash, the more it becomes your crutch.

Teleport: Across the map ganking, returning to lane, tower defending. I would say it is situational.

Cleanse: Removes CC's...good, but if you're getting CC'd that hard, you're doing it wrong.

Clarity: If you choose this, uninstall.

Exhaust: Awesome spell, can save you, can allow you to get kills, if you don't like ignite, get this.

Revive: Eww.

Smite: You're not a jungler.

Fortify/ Clairvoyance/ Rally: You're not a support.

Doran's Shield - Buy this for early game survivability.
Boots of Swiftness - Necessary for successful chasing/ganking.
Elixir of Fortitude - This is a cheap boost to health and attack damage early on, it is worth the investment.
Sheen - Buy this in at-most two pieces, the AP then Sheen, NEVER the mana crystal.
Trinity Force - After you get your Sheen it is easy farming from there on, so this shouldn't take too long to build. Also this IS your core.
Infinity Edge - Another piece of your core, expensive, yes. However each piece can be bought one at a time and all are wonderful items.

Now you can take one of two routes:
One - Build Hextech Revolver then Hextech Gunblade. This route is preferred as Morde's damage is mostly magic. 25% Spellvamp is just hot. Not to mention the slow and additional damage.

Two - Build straight for Bloodthirster. This is an okay route to take, especially if you're taking very little damage and want a nice boost to your own.

After you chose which to build first, then proceed to build the one you didn't build.

Then choose between Bloodthirster and Will of the Ancients



There are other items you can build, but these have carried me (and my team) through many many wins.
Just find combos that you like.

Very Simple.

Same sequences going against one or multiple enemies:

Creeping Death on you or an ally

Mace of Spades Whenever it is off cooldown

Siphon of Destruction When you can hit more than one target OR can get a killing blow.

Children of the Grave Important. If you're killing your team, land it on an AD carry. If you've been jumped and your health is low, put it on the tank, this should allow you to restore health to get away, or even turn the tide of the fight.

At level 7 or 8 you should be able to solo dragon and keep your shield up constantly. Also, you've become the most effective pusher on your team. You should be able to wipe out a minion wave in as little as 3 seconds, and can solo any jungle node.