Countering a Terrorblade

You can't just manfight Legion Commander 1 v 1. Even if Terrorblade can out-DPS her without his illusions (which he probably can't), She'll just pop Blade Mail and he'll just hit himself. No BKB allowed, Duel is instant.

Storm can kite around BKB perfectly well. Tinker... a bit less, but he has infinite Ghost Scepter to make up for it (seriously rearming ghost is just as imba as rearming BKB, volvo pls).

I think the huge problem here is Sunder

I personally think he is countered by kiters, which leads to my Drow Ranger pick. She have a slow, and a knockback/silence to maximize kiting.

But Metamorphosis is ranged

True, but any hero that can out DPS Terrorblade is subject to sunder.

I actually liked that Legion Commander pick, Hamstertamer. On paper she looks good. She can clear illusions(plus Battlefury maybe), AND she can mute enemies for 5 seconds. Problem is, if you can't kill him before Duel ends, he can just Sunder back.

He's so so so so squishy. He has ess Hp than a Sniper. Just get tons of good nukes and burst damage. A Tiny might be good.

I mean, the best way to counter Terrorblade is to grab aggresive supports and make life hell for him in lane. The moment he farms say a Yasha his farm accelerates and he will very rapidly take over a game. Which means the best way to counter him is to delay that Yasha.

Ganking him multiple times to force the opposing team to rotate, and delay that Yasha by 5-10 minutes gives your line-up more time to come online, and thus increase the odds of winning against the slit push.

I mean, his squishy nature is most evident in early lane (Since he naturally builds a rather quick Skadi, he doesn't stay Squishy for long)), so it's best to try and punish him for that then.