Some of the clip in the Monstercat video is from the game Bioshock: Infinite. This is because the song was originally used for Bioshock: Infinite trailer.
To find a remix, find the artist's name under the alphabetized list. All of the artist's remixes are listed with their name. For example, Morgan Pages's remix of 'Downhearted' would be under the 'M' tab, since the artist's name begins with the letter 'M'.