Test_World566612 is a world with all of the unreleased/scrapped/test enemies on it. It has one Gigantic Battlefield and one instance. To get there you must be level 20 or higher. The launchpad is in the Ninjago Monastary Ruins on Crux Prime.
A Freak Darkling, an unreleased enemy.
A Corrupted Mower, another unreleased enemy.
A Mace Stromling, another unrealeased enemy
A Malestrom Ninja, yet another unreleased enemy