Top counters for Nasus?
Since a lot of people seem to struggle with how to deal with him, I'll give you a few pointers.
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Stop playing lane bullies that don't exist outside of level 7. It's cool that Darius and Teemo punish you from level 2, but they can't itemize pure damage or else that's just a free gank waiting. Now on the other hand, people like Vlad, Gnar and Olaf have the harassing suppression to keep him down and can literally live in top lane until the rest of their team eventually shows up.
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Time is not on your side. If you aren't knocking down his ALLIES' (not his) tower by the time he gets an item or two, its a downward spiral. Your jungler not showing up the few moments he wasn't under his tower? Regret. Backing over pushing? Stack city. Stack stack city.
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His team is his biggest weakness. If his team cannot understand that sitting under a safe objective while Nasus pushes a lane, abuse it. Ride that 1/5 Jinx to the bank and farm her for money. Transition their lack of waveclear and numbers into a tower. And then another. And then an inhibitor.
Now for how to play AS nasus.
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Acquire a way to stay alive in lane until you run out of mana for the first time. DO. NOT. RUSH. SHEEN. With certain mastery set-ups, you can aim for Glacial Shroud + Kindlegem to get you to either 30% or 40% within 8 minutes and focus on stacking the entire game rather than surviving until Frozen heart at 15 minutes.
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Losing some cs to not get chunked for health is always better than dying. If I'm going back, I will toss down spirit fire and get a few extra gold then back and teleport into safety.
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Ask for a gank. Believe it or not, Wither is crippling. And even more crippling when a Xin Zhao jumps on you while you do that gerbil-powered-computer-loading-screen run to your tower. Burned flash? Doesn't matter. You're not getting anywhere. Then they come again and give nasus free gold. Works better if lane bullies (COUGHCOUGHTEEMODARIUSRUMBLECOUGHCOUGH) can't run away (Fk u riven).
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Spam the crap out of pings and tell your team to back off of any fighting until you actually reach a tower. Then they can be fodder for all you care. Use them as bait for +6s. If they make this game a challenge, get your money's worth out of them.
With these tools, everyone shall find the cane much easier to play around.

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One of them being Riven
) - better hp pool and solid damage.
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or
or 

or
depending. Especially as an AD champ, he will almost always rush 


makes a good