Honestly, Tahm has so much utility, innate tankiness, and huge amounts of damage... It's disgusting. Getting health increases your damage on everything by up to 8% of your bonus health. His Q does a ton of base and scaling damage, plus up to 8% of your bonus health, which is usually around 2kish late game, so that's an extra 160 damage just for building tanky on every single AA, Q, and when you press W. W is a 32% max health, 3s stun that only has one weakness and that's a QSS, but even if you QSS, you still take the health damage on top of the 8% of bonus health, plus 2% max health per 100 AP Tahm has. To make matters worse, Tahm has 'grey health' when he takes damage that's proportionate to the damage he's receiving, so his bubble's scaling in a normal team fight where he starts at full is 100% of missing health. That means you have to virtually kill him twice. To make things even worse, he can choose to grab a carry and whisk them away to safety with a huge speed boost while he negates Zed, Vi, Syndra, Veigar, and many other single targeted ultimates just because he ate them and it's not like he takes the damage despite the projectile, or fist, hitting him in the damn face. Seriously. The balls from Syndra's R, the giant deathball from Veigar's R, and even Vi's fricken fist will hit Tahm in the face still, but it won't do any damage to the one targeted nor to Tahm. Personally, I think Tahm should be hit by what ever the person he snags is targeted by. If Vi is charging at that carry that's eaten by Tahm, I could only imagine she'd just uppercut the carry out of Tahm's mouth or at least uppercut Tahm and if there's a bunch of balls being thrown at a carry and Tahm eats the carry and not the balls, you'd think he'd be smacked in the face by those balls.
Seriously though. If Tahm W's some one who's about to be hit by a targeted ability, Tahm should be hit by instead so he's not a 6s Zhonya's with a 6s CD. I want him punished for trying to save a carry who was about to be punished for being caught, none of this Tahm pressing W, getting a HUGE speed boost to escape.
When Tahm was released, the dev team was all like 'Yeah, he can be used to deliver people and save the carry or eat a high priority target' when in reality he's just a 'Ima eat the carry to cancel out all your CC and damage' and a 'Ima eat this Fiora who's trying to dive into us and 1v1 her with ease'. He's used to save his carry from the few targeted CC's that are left and complete negate targeted nukes, then people defend it saying they don't want assassins in their game making stuff toxic... Just play against a Tahm as anything that isn't Darius, Garen, or a fed as heck Fiora.
No champion should have a good early, mid, and late game while providing as much utility as he does. He's got 2 different stuns on short CD's, a shield that makes him near unkillable in a team fight, and his R has a passive that gives him end game scaling like no other. His kit isn't overloaded, it's hugely overtuned and more toxic than S2 LCS Yorick and trust me when I say it was toxic. Yorick was removed from the weekly rotation and nerfed into the floor because his kit was pure toxicity incarnate. A brick wall in lane that could poke you down and he'd never die. Tahm is becoming that equivalent.
-sus. Expect when he will tongue-lash, count down the cooldown (its a flat six seconds), and orb-walk. You have a chance to get away from him. When he gets low, CC-lock him. He can't use his shield. Instead of complaining, look at ways you can counter him. He's much easier to counter than %max health true damage garbage CT loves to pump out.
is fine and working as intended. At most just reduce his base damages or HP scaling on his ultimate and he's good to go.
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ult.**
her ult shouldn't be on cooldown because he ate someone.
make it so he can't really do anything.
Champs with slows and %Hp dmg like 
(build a 
) chunk him down so his gray health doesn't do anything.
You can deal with him, but you can't just pick random champions. Gotta have a plan!
