Evolving Battlefields
Source GM Core pg. 78
While some battlefields are relatively static, allowing the PCs and foes to clobber each other until one side wins, complex or evolving battlefields can lead to far more memorable encounters. One of the most straightforward ways to create an evolving battlefield is with dynamic environmental features. Maybe the floating platforms that make up the room's floor shuffle around on their own turn each round, or various squares teleport creatures to different locations—possibly between two rooms where separate battles take place simultaneously. These dynamic features have some overlap with complex hazards, though they don't tend to be an opposition or obstacle specifically threatening the PCs.
Similarly, a third party in the encounter, perhaps a rampaging monster or a passing security robot, could pose a danger to both sides but potentially benefit either. For instance, perhaps the PCs or their foes could harness this third party as a dangerous but powerful ally with a successful skill check of some kind or by making a risky bargain.
Sometimes the evolving battlefield is more of a state change, or series of state changes, and less of a constant presence. For instance, defeating the rogue AI controlling a space station could cause systems aboard the station to malfunction, perhaps turning off the artificial gravity and forcing the PCs to deal with the remaining robots while floating. Major physical changes to the environment, such as the collapsed portions of a room rising and falling or water beginning to rush in and fill the room, can force the PCs to rethink their plans to handle the new situation. Sometimes the evolving battlefield is more of an unexpected plot twist that occurs in the middle of the encounter. Perhaps the evil tyrant reveals that they were a dragon all along, or security robots arrive to help whichever side is outmatched. Whatever you choose, make sure it changes things up and makes the encounter feel more dynamic and different. For instance, raising up a portion of the battlefield that isn't particularly relevant when neither the PCs nor their foes are likely to care is less interesting than raising up the pedestal holding the datapad the PCs and their enemies are trying to recover.
Similarly, a third party in the encounter, perhaps a rampaging monster or a passing security robot, could pose a danger to both sides but potentially benefit either. For instance, perhaps the PCs or their foes could harness this third party as a dangerous but powerful ally with a successful skill check of some kind or by making a risky bargain.
Sometimes the evolving battlefield is more of a state change, or series of state changes, and less of a constant presence. For instance, defeating the rogue AI controlling a space station could cause systems aboard the station to malfunction, perhaps turning off the artificial gravity and forcing the PCs to deal with the remaining robots while floating. Major physical changes to the environment, such as the collapsed portions of a room rising and falling or water beginning to rush in and fill the room, can force the PCs to rethink their plans to handle the new situation. Sometimes the evolving battlefield is more of an unexpected plot twist that occurs in the middle of the encounter. Perhaps the evil tyrant reveals that they were a dragon all along, or security robots arrive to help whichever side is outmatched. Whatever you choose, make sure it changes things up and makes the encounter feel more dynamic and different. For instance, raising up a portion of the battlefield that isn't particularly relevant when neither the PCs nor their foes are likely to care is less interesting than raising up the pedestal holding the datapad the PCs and their enemies are trying to recover.