Replying...
Intro. It is an 18+ version of MLP: FIM (Friendship is Magic/Generation 4) which tells a more practical story, with less singing and more action. Just because it is 18+, it does not mean that it is straight up porn and swearing (like most AO games are), while there is some sexual scenes and curses, it has also darker topics, like death, revenge, depression, loneliness, existential crisis, gore and more. There are some differences here from the original show for kids. For instance, in the main show, Twilight Sparkle gets sent by Princess Celestia to live in Ponyville to learn about friendship, after Twilight and the other 5 ponies, which include Rainbow Dash, Fluttershy, Pinkie Pie, Rarity and Applejack defeat Nightmare Moon by using the Elements of Harmony within them, therefore bringing Princess Luna back from her evil form. In Friendship is Mature, however, Celestia doesn't tell Twilight to learn about friendship, and Mane 6 don't defeat Nightmare Moon, because Celestia did that earlier.

My Little Pony: Friendship is Mature

@Omoya