The Ancient Monster is the boss fight of the video game The Dog Island. He is a magical monster.
The Ancient Monster is first seen in the Kunka Ruins. He drops from the sky, and tells you you look like someone that has sealed him up in there before. Petasi tells you you have to jump on the switches to defeat him.
After you sniff and jump on the right switches, he falls a part and is defeated. He is thought to be sealed up, but then he gets back up. Petasi then comments that he had heard about something like this. He said you have to find a hidden switch to seal up magical monsters.
You find the switch in the middle of the room. The Ancient Monster spots you and runs up to you, but you jump on the switch. He then falls a part, sealing him up for real.