This was an extremely powerful black knight spell on cythera. The ability to enter on a target was only half of the spell. When you entered this realm of darkness, you remained there until you entered on the target...but while there you regenned at 2x your normal rate. Perhaps this part would be neat to implement.
As for the entering on target part...I like the same continent idea. Another way to alter it might be to enter on a player that accepts your entrance. This should work across continents because as armand mentioned, darkness falls upon the entire land, not just one continent. This should not be too overpowered either due to the soon to be implemented portal transport system.
