Here's a list of useful IDs and whatnot for various objects in The Beneath that can be handy to have around when configuring a modpack (or something along the lines of that). This information is applicable for Minecraft versions 1.10.2 through 1.12.2.

Biomes

Name	ID
The Beneath	beneath:the_beneath

Dimensions

Name	ID
The Beneath	10

Entities

Name	ID
Shadow	beneath:shadow
Hand	beneath:hand