To me, Malzahar is more of a utility champion than a full powerhouse runner. If flash is down, you're screwed. So 9/0/21 will help you dish out damage AND get away.

Athene's Unholy Grail : Mana regen, Cooldown Reduction, and 80 ability power. This item is AMAZING.

Will of the Ancients : 70 ability power and 20% spell vamp. Plus you give your teammates some AP and spell vamp also.

Berserker Greaves : WTF? Listen to me, 20 magic penetration is useless in the long run. 20 magic resistance isn't going to be the wall between you and a dead enemy. The extra attack speed is there so you can get Malefic Visions bouncing around minions. Mercury Treads are an option, but again, 20~ish magic resistance isn't your saving grace.

Rabadon's Deathcap : A little boring. This is on EVERY dedicated AP, but can't get around it. It is an AMAZING item.

Deathfire Grasp : Some AP, CDR, and a KICKASS active. If you get full build, this will do nearly 50% of the targets health!

Hextech Gunblade : Um, what? Okay, listen. With full build, you'll have 600+ AP and 160+ AD, murdering towers and not leaving you useless when your skills and actives are down. Plus, MORE spell vamp. And another active. You won't be left hanging.

Ignite - Honestly, I don't like getting this on EVERY SINGLE mid lane champion, but it gets the job done past turret.
Flash - Possibly Malzahar's ONLY escape tool, you CANNOT let this go to waste.

Other considerable spells:
Teleport : There's a jungler, right?
Promote : People still use that?
Clarity : Ever hear of Malefic Visions? ;)

This is fairly easy. At the start of a minion wave, look for an enemy minion about to die. PopMalefic Visions on that one and watch it bounce. Each bounce refunds and gives you back mana. Basic attack the minion with visions on it. Null Zone might help if it bounces on the big minion. DO NOT reuse Malefic Visions on a group of 3 or less minions, you'll just waste mana. Berserker Greaves make farming with Malefic Visions SO easy.

Early Game: Grab aMeki pendant, Health pot and Mana pot. They're there for mana problems and if the enemy mid is aggressive. Pop Malefic Visions once or twice every minion wave and keep mobile. Avoid getting hit and don't be afraid to move back if their mid is moving toward you. Malefic Visions will still give you money and exp no matter where on the map you are. When you get 500+ gold, get your jungler to cover mid for a minute so you can get Chalice of Harmony. Every so often go back to shop to get your items and DO NOT stay in lane with 25% or lower health. That's just asking your opponent to pull off a ballsy flash and get a kill.

Mid Game : With Hextech Revolver and Kage's Lucky Pick, you'll get some VERY excellent farm. Getting 3-7 health every SECOND you'll screw over their mid with your ability to stay back and farm. Level 6. Here comes the fun.
Note : Don't be afraid to use Call of the Void on bushes, because they will give you temporary vision of that bush. Use it to see if there's a ganker.

Strategy 1 : Note that Malefic Visions will ONLY bounce on the enemy champ if they're in range and/or there are no other minions to bounce to. If it does bounce on them, flash in, put down Null Zone (optional, deals INSANE damage if it lands), and use Nether Grasp. If they don't die, pop ignite and/or another Malefic Visions.
Note : Do NOT do anything while using Nether Grasp. Moving, Right Clicking an enemy, even using ignite (if they're not in range) can and WILL stop Nether Grasp. Though you can ignite the enemy and still have Nether Grasp going if they're in range of ignite.

Strategy 2 : If they let their guard down, go in WITH your jungler and pop Nether Grasp. Even without Null Zone, your jungler should be able to dish out some damage.
Now's when the "laning phase" ends, so don't be afraid to leave mid to go help other lanes.

Late Game : Team fights. Oh boy. You'll probably be a target since they think you won't have health because you don't have Rylai's or Rod of Ages, so if someone charges at you, put down a Null Zone and Nether Grasp. Even if you don't use Null Zone, your teammates are there. It's a kill either way. If one of YOUR teammates rushes in, they'll be targeted, so look for a distracted champion with fairly low health/defense, Nether Grasp them, and pop Malefic Visions and/or Your text to link here...ignite. Your teammates should see this and go for them as well, but if they don't, hey look more distracted enemies. PoppingNull Zone and Call of the Void will do SO MUCH damage (12% if their health) and silence them. MORE KILLS!

I've had a lot of fun with this build and I've gotten some pretty good scores with it (13/3/20). This build can work for other AP's (and well, I might add), but I think it personally fits Malzahar.Malefic Visions is just an AMAZING source of farm and money, I love it. I wouldn't say it's OP because the bounce range and low damage early game. Voidlings and basic attacks will keep it bouncing, but it can't do a lot of damage to big minions or champions. I'll be honest, I don't use Call of the Void unless I want to use a small poke to the enemy champ or check for ganks. But feel free to try to aim that thing and dish out more damage. Thanks for viewing, and votes up if you like it!

Focusing more in present health and percents than spell vamp, this revision requires you to constantly have blue instead of being the nice guy and giving it to your jungler. Not much else really changes besides the masteries and items. Farming and strategies are untouched.