Arch-Dragons are a species of dragons that appear in Rune Factory Tides of Destiny. They seem to be on a higher order and status than regular dragons.
Tallyn is the most notable Arch-Dragon because she is the only one living on the island anymore, it is unknown what happened to the rest.
The Egg is what appears after Tallyn leaves Fenith Island, and it is basically the next Arch Dragon to watch over Fenith. The Arch Dragon in the Egg can be named by the Player.
Theory Warning: This section contains theoretical information based on the research of one or several other users. It has not been officially verified by creators, and its factual accuracy is disputed.
A possibility is that they are higher than regular monsters but lower than the god dragons Terrable, Fiersome, Aquaticus, and Ventuswill. Maybe the same status as the Pheonix race that Raven is descended from.