10% minus resistances. Against a tank with 300 Mres (Hi Rammus), which has 75% damage reduction from magic, that becomes 2.5% of his HP per hit.
The thing to keep in mind is that anything you have should be hitting a squishy harder than it hits a tank. Assuming a squishy carry (hi Ashe) is running around with a base of 30 Mres and 50 from a Banshee's Veil (44.444% damage reduction), you'll knock a larger relative amount of her health and get more mileage from your fairly-small-but-still-present physical damage stat.
I can think of very few times you should be trying to down a tank before a squishy.
His ability at max level does 6%, and most people get Madred's on him so that buffs it up to 10%. His ability has a 0.01 AP ratio on it, which sounds horrible, but that's percentage max health, so with 100 AP it already goes up to 11%.
Note that this is also MAGIC damage. Couple it with his q, which reduces armor by 25, and an AD build, and he's doing 10+% of your HP in magic damage per hit - MagicRes and around 400 attack damage per hit + crits + armor debuff - remaining armor.
The thing is is that you can chunk out health with Kog'maw before super late tank builds of ridiculous armor and magic res (I do understand the approx. 400 AD is super late build, but less late for Kog'maw who can eat creep waves compared to a tank that -usually- can't).
I would have to say that you have a good point, and it's still valid, but Kog'maw seems to be the best out of the carries in taking out tanks.
Also note that you never focus tanks first with a carry (or shouldn't).
Also, 1000 AP Kog'maw builds are fun but in my experience too hard to pull off in a game. Yes, you can one shot entire creep waves with your ooze-ball of slowing pwn, and every attack chunks out 16% of the enemy's health, but you'll attack way too slow for it to be really good. Kog's Ulti does become a 300 MD+ spam-aoe-nuke, though, so that's always fun.
Psh, I never actualy jungled for srs so any jungling tips are apreciated, so thanks. I'll try the stupid funny build my friend gave me and talk to you on the results, if it does work as good as he says you'll have lots of udyr rape funtimes.
I'm also trying AP sion and Taric. AP sion for stupid burst damage, taric for being a jerk and never dying in lane.
Heal Spam Taric is funny to play because he refuses to die, but overrall the best Taric is Aurawhore. I've thought about an AD/AS build for him, but his AS is so atrocious to begin with I don't think it'd be worth it. If he ever got a slight buff to his base attack speed, it would work out so well with his +90 AD + heal ulti.