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Do not pick someone into him that depends on defensive itemization or a defensive steroid in order to function. That means no tanks or bruisers unless you're good at them. That or it's some overtuned asshole like Maokai/Ornn.
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Grievous wounds, as when his ult his down he relies on his sustain to keep himself alive.
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Do not try to fight him after he activates his ult. It lasts 4 sec, just back off until it ends.
That's it really.
Generally, he has the hardest time against ranged and/or AP opponents. Mobile fighters that rush damage can deal with him as well, but they can't put him out of the game completely unless their entire team is squishy for some reason.
Also, pay attention to what he's building. He scales the best with hp and cdr, so if he's rushing damage with no hp/defense, he's sacrificing teamfight potential and late game scaling for better dueling.
Honestly, top Troll is only good as a counterpick because, even if fed, his solo carry potential is low. He basically turns into a secondary support after the early game regardless of his build.