The Pocket Dimension is a blank dimension filled with nothingness. In order to get there build a nether portal but instead use iron blocks. There are two types of this dimension, normal and corrupted when Herobrine's head is attached anywhere on the portal.
There is no use of the dimension except when it is corrupted which can allow you to summon the 2 bosses, Steve and Nega Steve.
| Nether-based: | Collother | Darkness Dimension | Nether (Minecraft: A New Start) | The Quether | The Underworld | Voidwarp Nether
Overworld-based: | Carboniferous Dimension | Celestis | Clay Dimension | Devonian Dimension | GolemLand | Marsreegana | Misty Graves | Parather | The Alter | The Snare | Upside-Down Dimension | Voidwarp Mine