Not Updated For Current Season
This is my Guide for Malzahar, Prophet of the Void. I hope that anyone reading it learns something they didn't, and I hope you enjoy reading it as much as I did making it :D
To start things off, my summoner spells are a personal preference. Due to the mana gained from Malefic Visions (MV) you don't need clarity. I like to harass hard, so it suits me. Same goes for Ghost, flash is equally effective if not better. It is hard to dodge a flash/ult combo than it is a ghost/ult combo. It's just what I feel more comfortable using. Other options, such as Ignite, Flash or even Cleanse. Ignite is particularly nice, as you can cast it while using your ult without interrupting the cast. The choice is yours as to which you take.
Also, your starting gear can vary from my choice as well. Doran's Ring works quite nicely, with HP+MP regen+AP it is a strong choice. Mana crystal works as as well. I would avoid use of a boots+pots combo as you want to get your tear ASAP, this is also why I steer clear of Doran's Ring as well.
Now, down to business. Generally you want to take mid/solo lane. Malz is extremely potent mid due to his ability to harass from a distance, and his ult nearly always get him the kill (assuming you have been harassing up to lvl 6). Assuming you go mid, start slow. Avoid directly casting MV on your enemy as it eats mana for a limited effect. Try to work some minions down then have MV jump over them, returning your mana and hopefully jumping to your opponent. A great trick is waiting till a minion is super low when your opponent is near it, wait till the last second to cast on the minion. This way you get your mana and it's harder for them to out-range it. Also avoid using Call of the Void (CotV) unless they are extremely low and you think you can get a kill. This is due to its high mana cost and low dps at early lvls. The same rule applies to Null Zone (NZ). Hing mana cost and it won't do much unless they stand in it.. Concentrate on getting MV to jump as much and as often as possible. but there is a limit to this. Keeping your enemy constantly pinned to his turret is dangerous for you, so try to find a balance between safety and control. Your biggest weakness during the pre-ult phase is your lack or defenses. You have no way to regen heath apart from potions and no way to stop your enemy from hitting you. The best way I find to counter this is to give them a taste of their own medicine. Kat is a good example, her basic harassment combo is Bouncing Blade/shunpo, dodge the blade if possible, and when she Shunpo's hit her with MV and maybe a CotV if you have the mana to spare. You should make it clear that it isn't worth her while to harass. Jut like you, she has no HP regen. She doesn't have to worry about mana though, and that makes things difficult for you. You need to find a balance between mana/damage. This is why I pack Clarity :D. I can lay a smack-down to my hearts content without fear of running dry.
Ok, lets assume you've made it through the first phase of laning, you're lvl 6-8 and have one or two kills under your belt. Now you need to make a judgment call. Gank? Or Push? If your team-mates have their lanes pushed to the enemy tower, ganking is a waste of time. If your team is in the opposite position, then you are in business. With ult in hand, roll up to the appropriate lane and prepare to unleash hell upon your foes. Coming at your enemies at a perpendicular angle is optimal as it makes it easier to land CotV. Open with CotV to stop them from escaping, MV them and place NZ under their feet. Whip out Nether Grasp (NG) and enjoy. There are very few Champions that can survive your full combo, even if you still only have your starting gear. If your team is doing it's job then your enemies shouldn't be full anyways. Getting a double kill is hard, so don't bother trying. Single out the weakest/slowest, or the target without an escape method (flash/ any like effect) and make them pay for daring to play on your turf. If you are not able to gank, then things get a little bit more difficult. If your team has the enemy hugging their towers for dear life then you have virtually no chance of ganking effectively. If this is the case, then push...hard. Keep on top of M.I.A's and keep a vigilant lookout on the minimanp for enemy's not where they should be. All the the while you need to push your opponent right up to their tower and make them stay there. You can usually get of a bit of harassment even then, hopefully forcing them to Port home. Keep the voidlings rolling and beat that tower down ASAP. You should have your Tear of the Goddess stacking, and at least your Boots of Speed. If all goes well you should get the tower down before mid-game starts.
This phase is a little bit tricky. M.I.A.'s are harder to call effectively as the enemy is roaming about lots. You are squishy, have no doubts about it, but only a particularly stupid enemy with try to 1v1 you. So expect to be targeted for 2-3v1 ganks plenty. PLay it safe, roll with a team-mate. If multi-champ scuffles break out, your job is simple. Find the most useful/squishy/dangerous player on the enemy team, and melt their face off. Try to hit as many as possible with CotV, lay down NZ under as many people as possible. Then MV/NG your primary target. Once again, you are extremely squishy yourself and they will likely target you first. Make this work to your advantage, drop your basic combo, excluding your ult and run away. If you happen to have your Rylai's at this point, they will be slowed (yay for MV being a 4 second slow now) and your team should do the rest. If someone over extends trying to get you, make them pay by refreshing MV and letting rip with NG. Rinse and repeat as needed.
This follows along the same principles as Mid-game, only the stakes are higher. Your enemies will likely have some MR (that's what Void Staff is for) and their squishy-killing abilities with eat you up like a pizza at a weight-watchers convention. But the same tactic apply for your combo/ CotV/NZ MV/Ult. Feel free to throw around some extra MZ's as time permits. That concludes my guide, I hope it has proven useful to any/all who read it. And please remember, this is how I play, you might want to do it some other way. If you disagree with anything in this guide, please feel free to comment and let me know, I can change things as needed. Happy Slaying :D
A quick note about Void Staff. If your enemy has nobody stacking MR then VS is a waste. If I remember correctly, VS becomes more efficient than MP boots/Abysal Scepter at around 70 MR. So if nobody on the enemy team has 70ish MR, then get Abysal Scepter instead of VS. Using MP boots and AS can cause some enemies to have below 0 MR which will cause you to do bonus damage, and we all love more Damage :D