This is “Gummy King Tahm Kench” by RexSadio. It’s one of the many champion skin concepts that League of Legends fans love to post on the game’s official forums. It’s also a wonderful idea. That’s pretty much all I have to say about it.
For comparison’s sake, here’s what the standard in-game Tahm Kench looks like right now, as he’s tearing up the map in the 2015 League of Legends World Championships.
Screenshots via Surrender at 20.