Here you will find a collection of video guides (courtesy of Mizzteq, many thanks for her work) for the extreme trials in the game. The guides are sectioned accordingly by the expansions in reverse chronological order (most recent first).
Stormblood 4.X
The Four Lords
The four lords make their debut in FFXIV, but only three make the cut as extreme trials encounter with Genbu-ojisan sidelined.