To mix things up, I drew a 50x50 battlefield by hand with lots of collapsed walls, rubble, and other ruins.
As the PC's entered this part of the ruined landscape, they were fired upon by elite spectral archers (adjusted phantom warriors with the ranger template). I gave the elites powers intended to slow, immobilize, and otherwise root the onrushing PC's as the monsters fought a delaying action.
In a gigantic 50x50 area with ruins where the ghosts could simply shift through ruined walls and rubble while the PC's had to vault obstacles, climb obstacles, and run along the tops of obstacles to charge down their foes while being turned into pincushions, it turned into an epic fight.
Mix in story elements where the ghosts are elite skirmishers haunting the ruins, condemned to re-fight the same desperate delaying action against an oncoming army for eternity, and it was rather fun.
The players naturally whined about the enormity of the challenge when they first realized what they were being presented with, but really got into it as the combat went on. The dual-wielding ninja ranger especially loved all of the acrobatics and athletics checks for vaulting obstacles, balancing as he ran at full speed along the top of obstacles, and jumped around.
Overall, the party covered a LOT of space as they ran around the field, chasing the spectral skirmishers - who always tried to keep their distance where they could, using their ability to phase through walls and find new cover to their advantage.
Archer-based ranger templates also made the combat a SERIOUS challenge, given their sheer damage output. It was definitely a combat that seriously tested the party.
A lot of fun.
