There is apparently a PC game based off the series known as (Klay World: The Invasion), but sadly not much is known about it. All that is known is that it was uploaded on 2006 in Knoxs old website known as knoxskorner, and was helped made by a game company called Mocos Games. Not much is known about Mocos Games itself, but Klay World: The Invasion is apparently the only game they have ever made, as seen in their website here, and they also have a forum website here. In their website they say the idea was made by Knox, but Mocos Games design the game.
By what can be seen, the game is a first-person shooter as you play as a blue klayman in a room on a table, killing red klaymans as you collect items like weapons health and ammo, and to beat the game you have to meet another blue klayman with a hat under the table, and it will cut to a scene saying "You win!". There is also an easter egg of the main character of Benfer's unfinished film, "Villain"
The game is sadly no longer able to download, since Knox has deleted his website knoxskorner, and nobody has found any other website that has the download link of the game, and knox himself has not made any other comment about it. Mocos Games also seems to be completely abandoned by its creators.