Hey Folks, this is my first posted build so go easy on me!
Today I'm going to talk about Nasus, a very interesting champion for several reasons. First off, if specced right he can be used to single-handedly take out two or even three enemy tanks solo (trust me, it's hilarious). To get a good idea of how this is possible, let's look at his abilities.
First off we have his innate, Soul Eater. Right off the bat, you start off with a 10% lifesteal that goes up to 15 and 20% at levels 6 and 11 respectively. This will make your life (mostly) relaxing early game, assuming you still play moderately defensively. Once you get Atma's Impaler and start doing 200+ damage per hit, you're looking at getting at least 40 health back each attack. Not bad at all for an innate.
Nasus' first true attack (and the one you NEED to get first every time) is Siphoning Strike. This move starts off looking really bad. +30 to your next auto attack is kind of a joke. But the next part is pretty amazing. Every time you kill an enemy (any kind: champion, minion, neutral monster), the attack gains a permanent 2 to its damage. So as long as you get this right away and can time your last shots well, this number can easily give you an extra +150 to the ability's natural +110 at level 5. Plus, the cooldown on this one is very short (4 seconds at level 5) so by the end of the game you're going to be steamrolling everything.
His next attack is handy but kind of a throw-away in my opinion, at least until at least level 3. Wither is a strange slow that gets stronger as time goes on. Starting off at 35% no matter the level, each second the slow increases in power. So at level 5, you're slowing the enemy down 95% in the last second. Pretty handy but levels 1 and 2 make it seem real weak.
Attack #3, Spirit Fire, is amazing. This ability can win you team fights. Not only is it a ground-target AoE attack (which takes away some decent HP by the way), and not only does it have some nice range for a melee tank, but it actually reduces armor from Every enemy standing in the circle! And not just some small amount either: at level 1 it takes away 20 Armor. At level 5 it takes away 40! Add that to your armor penetration and tanks are going to be hurting a lot more than usual.
His ultimate is pretty tanky. It's also a key feature for killing enemy tanks - especially any health tanks or Vlad. Fury of the Sands turns Nasus into this big, hulking beast that gains extra health (300/450/600), gains a player-based AoE that drains enemy's hp (3/4/5% max) AND turns all health drained into bonus damage for you! It lasts 24 precious seconds. Do not use it at the beginning of a fight. Wait until there are at least 2 people around you so your AoE's doing what it's meant to - hit as many people as it can.
As far as the Runes go, I consider them very variable. I doubt a lot of tanks are going to use Mana Glyphs, but I find he's usually pretty lacking and this made up for it. Health and dodge are of course a must. You can swap out the armor penetration for attack damage if you're thinking of aiming for people other than tanks too.
The item list is pretty basic. The first two are right from his Recommended page, with the dodge on the Ninja Tabi working really well with your dodge glyphs (you'll be at around 20% dodge with them) and the increased mana regen (because Nasus really doesn't have enough mana early on) and magic resistance on the Chalice for some extra defense against those abilities people just love to use. In my opinion, Frozen Mallet is good on just about anyone - and with your move speed look at 390 there are going to be people outrunning you. FM helps to prevent this from happening. Atma's Impaler is absolutely CRUCIAL for any health tank. By the time you get it, your damage should be pushed up past - or very close to - 200. The Sunfires I threw in because they're such a fun item. If there are a lot more casters in the enemy group than tanks or whatnot, feel free to swap them out forr something like a Force of Nature and maybe a Banshee's Veil.
To start off: Be defensive. You're not made to tower rush, at least not at level 1. Play it safe and get as many last shots as you can with your Siphoning Strike. Defend your ally whenever possible. Remember, you are not the carry. You can hurt like hell end-game, but a carried Twitch, Xin, or Yi will always outdamage you. Let them get champion kills if possible. Harass the hell out of the enemies with your Spirit Fire. If they're stupid and stay in the Fire, hit them once with your Siphoning Strike while the armor debuff is still on them. 9 times out of 10, a smart enemy will run after seeing a huge chunk of their health get knocked off in "one" hit.
Same sort of strategy as before, but a little more aggressive now. You should have a couple items at your disposal and with your ultimate you can turn real nasty in a fight with the press of a button. Do not solo enemies yet. Always defend the carry.
By this point you should have your Atma's Impaler - and if you timed your last hits right, your Siphoning Strike should be at least +120 extra damage. With this combination, your enemies are in for a world of hurt. Expect to be doing 400 damage every 4 seconds to the people you're fighting (yeah, I'm not kidding. It's terrific), more if you remember to Spirit Fire them. If you get into a group fight, pop your ult and whale on the tanks while the carries take out the other carries. I guarantee with your ult, Atma's, and a well fed Siphoning Strike, you will kill any tank at this point. But don't forget you're still a tank. Defend your carry if they're in trouble.
I hope this gives you folks a good feel for the kind of intense pain I usually lay down on my enemies when I play Nasus. Good luck, have fun, and please comment/criticize this but remember it's my first build! :)