Kog'Maw bolsters one of the longest ranges amongst champions, making escaping rather difficult for champions like Shaco and last minute Flash attempts. On top of that, his passive allows him to bomb enemies for true damage of up to 525 damage. These put together create a champion that can spit acid on enemies constantly when harassing enemy groups.

Caustic Spittle
Your armor and magic resist debuffer skill that also deals moderately good damage, with a AP ratio of 70%. Most importantly, this skill grants bonus passive attack speed of up to 30%. This makes the skill very important for AD carry Kog'Maws and AP DPS Hybrid Kog'Maws.

Bio-Arcane Barrage
The bread and butter of his superior harassing capability, this skill adds 210 range to his natural 500 auto-attack range. As an added effect, his auto-attacks get magic damage equal to 6%(+1% for every 100 AP) of the target being attacked. Essentially this means a free, extra powerful Madred's Bloodrazor. With this skill active, Kog'Maw can essentially tear apart both tanky and squishy targets. The only limiting factor would be can Kog survive long enough to inflict the damage.

Void Ooze
Amazing slow ability, maxing at 60% speed reduction, this will be a team get-away solution that will delay most champions except lets say....Master Yi? It has very good AoE damage at 260(+70% of AP). With the amount of range on this skill and it's ability to damage everything consistantly makes it very effective at dealing heavy punishment on mobs.

Living Artillery
This is the very reason people fear Kog'Maw, he has an ability that can be spammed when necessary once Lv6 hits. As an added bonus, it reveals anything it damages for a couple seconds; thus allowing for follow-up shots for potential unsuspecting kills. Coupled with it's relatively low cost to cast if you wait for it's stack to expire, it can be used both defensively as well as offensively. Ever had a bush that seems dangerous and you want to check it? Artillery it and see if anything is inside! The range of effect increases drastically with every level added to this skill, to the point where it stretches from the top of your screen to the bottom.