The Ender

The Ender is the last main dimension. One is unable to reach it unless he has beaten all the bosses of the other dimensions. It's swarming with enderkind, and has strange physical properties. It is not a slip of the Overworld, but it's own dimension entirely.

The End is currently available in vanilla Minecraft, but lacks in content and only things unique are endstone and the Enderdragon. But the AllDemDimensions mod is going to change that. The Ender will be separate from the End, in that the Ender will have a lot of content, but the End will simply be a fighting area for the Ender Dragon.

Terrain
The Ender composes of large, floating chunks of endstone. If one falls of an island and there is nothing beneath him, he will fall into the void and die. The Ender's notable feature are large obsidian spikes.

Portal
The Ender portal frame is made of a special block, which is made of one of each top gem from every other main dimension: One diamond, one ruby, one sapphire and one emerald.

An Eye Of Ender is crafted differently to the Vanilla version. The player must first obtain four Endstone dust from Enderbarons, a neutral mob, that when attacked will emit a rallying call to all endermobs within a certain radius. Then the player must battle with four Enderlords, a powerful brute of an Endermob, to gain an Essence Of Void. An Ender Pearl surrounded by four Endstone Dust and four Essence Of Void will create an Eye Of Ender.