Shadow Arena

Shadow Arenas are large, naturally generated structures found exclusively in Voxrokrania, one of the three side dimensions of the Shadowlands. There are always five generated per world.

Appearance
Shadow Arenas are composed of Voxstone and Dark Bedrock and are giant, circular domes with a small entrance leading into it, resembling somewhat igloos. Once entered, the entrance seals itself up. The only way to get out is to defeat all the waves of Shadowlands mobs that are released to fight the Player.

Wave Mechanics
There are always 3 waves, and for each arena, there are completely randomized mobs. The first wave always releases 5 mobs that are all the same species (it is randomly chosen between Cerysl, Voxrokauts, and Sinister Vytls). These mobs drop double the XP than normal and double the items. The second wave always releases 15 mobs that are of three different species (one of these species will always be Voxrokauts, and the other possible two are randomly chosen between Cerysl, Fire Cerysl, Sinister Vytls, and Endermen). These mobs drop triple the XP and items than normal. The third and last wave releases 50 mobs that are all the same species (it is randomly chosen between Voxrokauts and Fire Cerysl) as well as a half-healthed Ender Dragon once all 50 have been killed. This Ender Dragon cannot break the Voxstone or the Dark Bedrock that makes up the Shadow Arena. Once all three waves have been conquered, XP will shower on the arena as well as 50 Shadow Keys, 25 Dark Coins, and 10 Diamonds, and the entrance will open back up (as well as stay open).

Location
Shadow Arenas are only generated in Voxrokrania and can be between 10,000 - 80,000 blocks away from each other, which will require some time to search out each one in order to defeat all 5.

Trivia

 * Since Shadow Arenas are so incredibly difficult, it is only possible to defeat them with (at least) a full diamond set or better. Enchantments will become almost necessary.
 * The battle music that plays when the waves start coming highly resembles Coldplay's Clocks.