Hi, I would like to speedrun the game Mortal Kombat Kollection on PC via Steam, but I can't find this game on your website.

The Arcade Kollection is just a re-release of the older games, so runs for those games just go under the normal leaderboard for the game (so if you're playing Mortal Kombat 2 in the collection, you just submit your run to the MK2 leaderboard).