For the upcoming Dragon's Dogma, Capcom has revealed the presence of a legendary dragon known as the Ur-Dragon (not related to the Magic: The Gathering card above, unfortunately) which can only be slaid by combining forces with all players who face it.
Appearing "in the Everfall beneath Gran Soren", the Ur-Dragon has so many hit points that it will take everyone and their party of Pawns to slay the beast in an asynchronous encounter where "the effect of each party's attacks will be combined". Capcom does warn, however, that "it will take multiple encounters before the Ur-Dragon finally falls".
All players will receive a substantial loot drop for contributing to the battle, and the one who deals the finishing blow will get the maximum reward. The names and play times of all who contributed to the death of the Ur-Dragon will be recorded in a hall of fame.
The Ur-Dragon will be available at the launch of Dragon's Dogma on May 22 in North America.