Queen Chrysalis has had enough of the mane 6's meddling. So, she casts them into a different dimension with her green fire ring. Where they end up is not her concern.

The mane 6 find themselves in Terraria, a sandbox land. (This story assumes some familiarity with the game, but it's not required) Follow them as they come to term with their new 8-bit selves. It's not as easy as one might think. Pinkie can't make friends with the guide and Fluttershy has a real problem with the slimes killing her bunnies. Twilight and Rarity can't use their magic like they used to and Rainbow Dash cant fly (yet). Only Applejack seems to be at home. Until night falls.

Read as the ponies come to term with killing things and making their own world.

For those who don't know, Terraria is a 8 bit, 2d sandbox game that focuses on building and monster slaying. It has a range of monsters to kill, including bosses. It also has a range of materials to collect to build fortresses and armor. Go here: http://wiki.terrariaonline.com/Terraria_Wiki
If you have questions about a specific thing or entity.

ALSO a huge thanks to poochyenawolfy for letting me use her 8bit ponies. Go check out her deviantart.