This team is centered on the synergy between M-Diancie and Chandelure. M-Diancie helps keeps Stealth Rocks off the field for Chandelure, while Chandelure pressures steel types which will commonly check M-Diancie (Celesteela, Magearna etc..). Coverage on both is pretty standard, minus Psyshock on M-Diancie which is primarily used to pressure M-Venusaur which is crucial for Keldeo to break through many teams.
Fightium-Z CM Keldeo is a cool set and it shares many checks with Diancie (Toxapex, Gastrodon, M-Venu, etc..), allowing one to break for the other.
Ferrothorn provides the team with SR and a strong defensive backbone to fall back on. Chople berry is key to improve the matchup against strong fighting types who can otherwise be a problem.
This particular Lando set was added to improve the match-up against stall as dugtrio is usually able to trap Diancie and Keldeo cannot reliable break stall on its own. Also provides intimidate, ground-immunity etc..
Scarf Latios proves speed control and defog, checks things the team was otherwise weak to (Keldeo), and can trick things which is always useful.