Guild Wars 2

Also as far as the Dwarfs why not have the story state that some got sucked into the swirling pool time traveling them into the story line right from the Hall of monuments.

:)

It is very easy to incorporate the Tengu or any other “new” not present in the pact or original story line.
For example lets take the Tengu, although they hid behind walls Arena net can introduce the story that a few rebelled against the majority and left the walls to help the fight against Zhaitan.
Like this it will be easy to explain why the race isn’t seen fighting with the pact. It could be explained that some rebels/renegades left their homelands and came forth to answer the call.