Hello!

Only my second guide, but my first guide for a champion I actually play! So be nice. ;)

AP Kog'Maw is one of my favourite champions... he's really fun and at the same time satisfying. I wall warn you: you need to be good with skill shots.

The two guides provided are
1) Goal Build
2) Newcomer Kog'Maw / "I'm not getting the Blue Buff" / Doing Badly

For first time AP Kog'Maw, I recommend build 2 whilst you learn his skill shots, as until you're good you will need the extra mana. But Morello's Evil Tome is definitely superior to Archangel's if you can manage your mana... simply for the CDR and AP you wouldn't have until later in the game with Archangel's.

Using his auto-attacks is something else you need to master! ...they are still a good source of damage.

Pros:

• Strong early game / not a late-game champion.
• Optimises his kit by utilizing the AP scalings.

Cons:

• More squishy - spell vamp versus life steal.
• More slow - I don't recommend Lich Bane on AP Kog'Maw, as such he has no real speed options.

Bio-Arcane Barrage is actually comparable between the two, contrary to what some might tell you. Whilst it's true that Ranged Carry Kog'Maw might be dealing 10% at ~2 attack speed (6% + Madred's Bloodrazor), with late-game AP an AP Kog'Maw is dealing 12% at 1.4 attack speed (the AP ratio and attack speed from Caustic Spittle)... which is still pretty good damage from an auto-attack on a caster.

Pros:

• Easy skill order - whereas a lot of casters have to choose between utility skills and damage skills, Void Ooze is a potent slow and half his damage all in one.
• Double-up harassing and farming - Void Ooze functions to half health both the champions and minions it hits.
• High burst damage - point-click Caustic Spittle and a pass-through skill shot ( Void Ooze) means it's not difficult
• Artillery - absurd range!
• A very low cooldown ability - Twin Fang, Living Artillery, etc, are rare cases of being able to kite with abilities...
• Element of surprise - many people don't know what to expect.
• Satisfying to play scoring that last hit with Living Artillery, knowing the enemy is desperately trying to get out of range, etc.

Cons:

• Very weak against gap closers - such as Xin Zhao and Ahri
• Very squishy - the artillery mentality is "go class cannon, because you're dying if they catch you anyway".
• Very slow - due to his Ranged Carry brother, he has a Ranged Carry base movement speed.

My preference:

• Flash - Let's face it; any champion without an escape mechanism needs one.
• Teleport - Underrated, but I find it invaluable. Particularly useful against champions like LeBlanc and Veigar, where it's better not to risk sticking around.

Good choices:

• Ghost - A good alternative for Flash, and can be particularly useful for "kiting" with your ultimate.
• Clairvoyance - Until you get good at landing Living Artillery blind, this is a possibility.
• Surge - Free attack speed and ability power.
• Clarity - Perhaps even recommended until you get good at managing your mana.
• Exhaust - Most useful against a fighter-heavy team or if you're up against an assassin. Kog'Maw has no issues against AD Carries though, not when it matters.

Bad choices:

• Ignite - You plan on being in range? But seriously, only if they're healer heavy.
• Cleanse - They've caught you... you are dying.
• Revive - No.
• Smite - No.
• Heal - Not really needed...
• Promote - No.