by Mike Shea on 15 March 2010
The Dungeon Master's Guide 2 is likely the best D&D 4e book published for Dungeon Masters. One of the great additions to this book, and to the 4e system in general, is the concept of "environmental powers". These powers let players interact with their battle environment in unique ways. Examples include throwing explosive barrels of strong dwarven mead, rolling large boulders upon your foes, or firing large ballista at a dragon.
These environmental powers are an important addition to the tools available to dungeons masters. It is more than a small feature to throw in from time to time - environmental powers can keep your battles fresh and keep your players excited.
There is unfortunately very few samples of environmental powers in the DMG2. Fortunately, it is easy enough for us to make new ones. Pages 65 and 66 of the DMG2 have all the tools we need to design environmental powers of our own. Need a ballista to fire flaming bolts at the white dragon? Give it an attack of level+5 vs AC and pick out the damage from the damage-by-level chart.
Even better, these tools give you the ability to add in on-the-spot environmental powers when your players come up with something interesting you weren't prepared for. Just make the attack score level+5 vs AC or level+3 vs any other defense and use the damage-per-level chart as your baseline for damage.
There is one major change you should make, however, that isn't covered in the DMG2. Make these environmental powers a minor action to activate, rather than a standard action.
Shrewd players understand the economy of actions and are unlikely to seek out environmental powers unless they can do so easily. Most players will stick to what they know, their own character powers, unless you entice them by making it easy for them to experiment. Making environmental powers activate with a minor lets them try it out without wasting a standard action. You can limit it to a single activation per turn or make it a one-shot effect if its particularly powerful.
Like terrain effects, environmental powers are a wonderful way to keep your battles fresh and exciting. They give some fun new options to your players and they add a whole new variable in your design. Each time you design an encounter, consider whether and how an environmental power might add some excitement.