Tahm Kench has been a problem in League of Legends for a while, either dominating the meta or being invisible. His kit is deemed overpowered for competitive games, and he received a host of nerfs to tame him down; that is without mentioning the Tahm Kench Toplane.
Season 9 brought multiple nerfs, leaving Kench as a dead Champion for Season 10; ending with a 45% win rate and a 0.3-0.5% pick rate. Season 11 has fared him much better either.
Riot did, however, announced a small rework which was delayed. However, in the Arcana skins reveal, fans noticed a slight change to some of the abilities. Most notably that the (Q) Tongue Lash applied his passive once more, which had previously been removed in a nerf, and his (R) Abyssal Voyage seemed to apply a knock-up.
The details of the rework are here, and SkinSpotlights has a short video to showcase the changes.
Tahm Kench's Devour has been moved to be an Ultimate, this was one part of the kit that made him so strong at competitive level due to the safety it offers allies.
His old Ultimate has been switched to his W, with the Abyssal Voyage becoming the Abyssal Dive. Allies can no longer join the dive, but it can damage enemies and has a knock-up.
Not only will his Tongue Lash now apply a stack of his passive once more, but it will now heal Tahm Kench as well as allowing players to Devour enemy Champions with it.
Spideraxe posted all the ability details which are currently on PBE onto Twitter. As usual, take these with a pinch of salt as they may still change, and numbers are likely to move about. Nothing is confirmed until it hits live servers.
The Tahm Kench rework is currently on PBE, so is scheduled to be on patch 11.13. It should therefore be deployed to League of Legends live servers from June 23rd.