Guild Wars 2

It would be amazing having a dragon dominating a Keep or a Castle and the 3 servers trying to conquer it and kill the dragon at the same time.

An overall unusual and much more hostile PvE in WvW could bring more action and objectives to it.

:)

That would be interesting but the only problem I see is that the particular castle or keep will be impossible to take, partly because each world will also attack each other and the over defense of the keep or castle; also the defenders of the keep or castle will have to also fight the dragon; making it impossible to keep if there are too few defenders.

A dragon dominating a keep? That sounds interesting. Maybe make it into more of an AI dominating a keep. Have random events where event centaurs or skritts would try to take over the keep if your server is dominating for too long.

+1 for comment above