Giant Abbys (abbys biome) + dimension Underworld

This idea of abbys is meant to be a giant (rare) biome with only just a giant hole in ground. 

It is suppose to be giant outdoor stronghold with new monster (mostly flying) and decent loot. There could be new weapons, blocks, plants, ....

At the bottom of the abbys is not going to be bedrock but new portal of the new dimension - Underworld.

Becouse bedrock was the wall that kept those Underworld monster from the outside world.

Underworld is suppose to be drained, lightless and scary place. In this world there are going to be new ghost like monsters. Something like wraiths or deadly shadows.

This idea is not very detailed it is just shell.

This idea is mostly inspired by anime ´Made in Abbys´. 

Im also sorry for my english im not from english speaking country and i hope you can understand it all. 

If this gets upvoted i will try to make full detailed post.