Cubed Dimensions!

There is a lot of potential for some brand new Mobs, Blocks, etc. To be added into the game as its own dimension however that may be too much work so I have an idea! they are called Cubed Dimensions, essentially you will be able to find a rare item called Unknown Gem after finding Unknown Ore. Unknown Ore is a little bit more rare than Diamonds, however you won't be able to make any armor or weapons. And if you use 8 diamonds to surround the Unknown Gem you will be able to make a Portal Gem which allows you to teleport into a small new dimension that will have a very unique structure or terrain. They will have new and unique hostile mobs that drop a lot of cool stuff that you might not be able to find in the overworld. Like new items, potions, armor, etc.

There are many ideas for themes and you could even add 1-2 new themes every update for new and interesting stuff. There could also be bosses that inhabit these "themes" and if you beat the boss. You would get a block that spawns in a small shrine in the overworld that allows you to easily travel back to the same exact dimension and you would be able to make a new base there and stuff however the mobs that you defeated and the boss will not respawn, neither will the loot. That way players will encouraged to find more Unknown Gems. And if you want you could even make it so that Unknown Ore only spawns after you defeat the Ender Dragon.