It is a boss level. Taking place inside the ruins nearby Happy Tree Kingdom, you face against the first boss, Intruder, a fierce-looking dragon that attacks by shooting eggs.
The boss room layout consists of a flat ground with two small platforms on the left side, with the leftmost platform being placed higher than the one on its right. Behind the lower platform and below the higher platform, there are two Heart items for health recovery. Intruder is located on the right side and moves up and down while shooting three eggs in a spread shot. After doing the basic motion a few times, it can also move forward, going for the lower platform, which can cause collision damage to the playable character if he/she isn't on any of the platforms.
To defeat it, one must shoot its head enough times. Defeating Intruder grants you access to the second kingdom in the game, Aqua Kingdom.