This is my personal Morde build. I use it quite frequently as I devised it myself and it never fails. Even if your team is having a bad game, it's quite easy to get a few kills and overturn the match on your own. It yields good laning sustain (try and get mid) and allows for some good damage output when harassing early game. Once you come up against the other team in a good fight, you should be able to smash them down with SoD and then target a good DPS enemy for CotG. I've had games with Morde that started out horribly with the others dying all over the place, and our jungler just running around doing nothing, with poor old me soloing top only to look on in horror. Naturally I always refuse to surrender @ 20mins, even if it's like 5/18. BeastMorde is only just getting warmed up @ 20mins. Word of advice, if you see Darius, clone that mofo, cos he will take down the whole team. So funny to watch their own Darius quadra/pentakill them. The key to BeastMorde is confidence. Know your roll, and trust in your ability to take and deal a tonne of damage and laugh maniacally as you rapas das bestas their entire team.

The beauty of this Morde is he's the baddest cat out on the field and no-one knows it yet. The second you can sneak away from your turret to join in a fight or gank, the other team will start to feel the steel. The secret to a good BeastMorde is cloning, make sure you clone someone good enough to help you in a fight. There's no use in cloning Sona or someone with no DPS. As I said in the intro, the Darius clone works great, his passive armorpen E skill eats through the other team and he's tanky as hell to try and bring down. Just keep an eye on your lane mates if your solo top or mid, and if you get the chance, sneak away and get the beast on with some unsuspecting victims. PRAY TO THE METAL GODS YOUR MOUSE BATTERY DOESN'T DIE IN A TEAM FIGHT.

I've had to add this section because for some reason MOBAFIRE's mastery window is showing the old masteries which aren't even relevant.

Offense = 21

3x Mental Force & 1 in Summoners Wrath
4x Sorcery & 1 in Arcane Knowledge
3x Havoc
4x Blast & 4x Arcmage & 1 in Executioner

Defense = 9

3x Resistance & 1 in Hardiness
4x Durability & 1 in Veteran's Scars

You can set it up however you prefer, but this always works really well for me. If it aint broke, don't fix it.

Skills are pretty self explanatory. Max SoD and Mace of Spades ASAP and take your ulti in between. Morde's Creeping Death isn't that great, but change your keybindings so you smart cast it on self with just W, best way to use it.

YES I GET SOME AD WITH MORDE. His Q skill hits for AD/AP so why not? And gunblade has the same spellvamp that Will of the Ancients does, so get that instead. Will of the Ancients is garbage, I can't stress that enough. Combine gunblade with a stacked bloodthirster and it's "Hello Shirley". I buy randuins for the extra health/regen/armor, plus you have a chance to slow their DPS's attack speed. All in all you'll be hella tanky and output a sh*tload of damage, AD and AP.

Ghost and ignite. When you know you can take the mid laner, rush them and Siphon+Mace then ignite then ulti = Free kill at lvl 6.

Pros:

Extremely Durable
Capable of beating an entire team with Children of the Grave clone
Can get into a fight, soak up a tonne of damage then run out and come back in full health again 20secs later.
Can overturn matches single handedly by just being in the right place at the right time.

Cons:

None that I'm aware of really :D

In summary, it's BeastMorde... need I say more?