Soo... Tahm Kench

I haven't played him myself, but initial impressions are that he's simply over-tuned while still being extremely difficult to play effectively.

• Tongue Lash has way too low of a CD for its high base damage on top of its ultimate passive addition.
• Devour's CD is too low for its massive utility. In any given fight, the carry can be inside him almost 100% of the time (or 50% of the time for enemies), making it very difficult (not to mention frustrating) to finish off anyone while he can store them away on command and act like some armored transport vehicle.
• Thick Skin's active makes him scale practically twice off of health (excluding his already present health scaling from his ultimate passive). The passive is fine, but the active needs to be retuned with only a scaling % of damage turning into Gray Health. It wouldn't be hard to redo the numbers while still keeping clarity about how much he's going to heal/shield.
• Abyssal Voyage can overall go unchanged, it has a healthy application since he can't effectively use it for escapes, and the range for a partner to "be taken along for the ride" feels comfortable.

If there had to be buffs for him to receive, it would have to be better Acquired Taste effects. It's difficult to apply in normal combat, and even then you've probably already used both abilities it uses to proc it. This passive may be the reasoning behind why his CDs are so low for his only readily accessible damaging abilities, but I think a way to counteract this is simply to give a bonus to his ultimate passive on applicable enemies on top of the normal benefits.

For those of you focused on his (low) win-rate, remember what Bard was like? We can probably expect the same pattern with Tahm Kench, especially considering how difficult he is.

TL;DR I think his CDs are too low on his [Q] and [W], given how much impact they have. His health scaling is much too efficient because of his [E], and his passive could be buffed as compensation for the rest of these nerfs.