Not to be confused by Eternal Island.
The Eternal Boss is the 2nd ever Boss to be introduced in Ninja Legends. The Eternal Boss is available once you reach the "Shadow" rank and above. The Ud’zal package is used as it's appearance. To battle it, players must go to the portal near the Robot Boss arena. It gives 5x the rewards as the Robot Boss. However, the Eternal Boss has 3,000 health instead of 2,500.
While battling the Eternal Boss, it might jump. If it does, upon impact, it will bounce you out of the arena, and can possibly throw you off the edge. This will prevent you from attacking it until you double jump back into the arena. There was a secret crystal located on one of the mini Islands on the right side of the boss. There was another secret crystal located on the mini island on the behind left side of it but since it was removed you can no longer see it.