Phantom Dimension

To make a portal you would have to make a structure like this

After you make the structure you would have to either put an emerald block, Diamond block, or Dragon egg

Then a black liquid will fill the box, if you go in you would find skeleton horses, Skeletons, Strays, Vexes and Phantoms

The only plants that spawn are on course dirt, wither roses, you can also find your lost pets when they die

Skeleton Cows, Skeleton pigs and Skeleton Chickens are hostile mobs and white liquid oceans called ectoplasm