Art of the Animal Mercs (used in thumbnail too at least for abc testing) was made by
IbisFloatingCat
Excellent work and check out more of their stuff (they may also do commissions - not entirely certain though)
https://www.reddit.com/r/tf2/comments/1qbajit/the_mercs_but_i_turned_them_all_into_animals_that/
Reddit
