One of my favorite rules in 3rd Edition is the “DM’s Best Friend”. The basic guideline is that that when faced with a situation that gives either an advantage or disadvantage to the PCs, assign a +2/-2 circumstance modifier to the action. This rule may seem obvious, but it codified something many Dungeon Masters had been doing for years. Having the rule in place encouraged players to try something inventive in order to get that bonus (or something desperate in order to get a roll, even if attempted with a penalty).
The “DM’s Best Friend” still exists in 4th Edition, but it is now joined by the improvised damage rules. This little gem is found on page 42 of the Dungeon Masters Guide (although you probably want to take a look at the DMG Rules Update, since the Difficulty Class values have changed significantly).
Improvised damage is used when the player tries something outside the scope of the normal rules. The DM basically determines what skill or ability check would govern the attack. The DM then determines if the task should be Easy (5), Moderate (10) or Hard (15), then adds ½ the character’s level (give or take a few). If they make the roll, the DM then picks a level appropriate damage value from either the Normal (can be repeated) or Limited (one time/extreme) chart. Viola, instant pseudo-power!
I love this rule because, like circumstance modifiers, it encourages players to be inventive and think outside the box. The example given on page 42 describes a rogue swinging on a chandelier to push an ogre into a brazier of burning coals. I am including some additional examples below to show the wide variety of situations improvised damage can handle.
The party is fighting a group of orcs when more start to come up a the stairway. A 6th level fighter decides to buy them some time. The DM had described two statues on either side of the stairs, so the fighter decides to kick one off its pedestal and down the stairs. The DM decides it is a Moderate (DC: 12) Strength check to knock it off its pedestal. The statue makes a Dex vs Reflex attack (using the fighter's Dex) against each orc on the way down. Since it is affecting multiple targets and there is a chance for a second attack, the DM decides it will do 1d6+4 (Low Normal) damage. The DM also decides that any orc hit must make a save or be knocked prone.
A 15th level warlock wishes to sabotage a permanent teleportation circle. Since he is trained in Arcana and knows the Linked Portal ritual, so the DM decides it’s possible. The DM decides the warlock needs to spend ten minutes, 100 GP of alchemical reagents, and make a Hard (DC: 23) Arcana check to alter it. The warlock is successful so the next person (or persons) to use the portal will take 3d10+6 (Low Limited) damage and the circle will be rendered inoperable until repaired.
The party is traveling through a mountain pass which the DM has stated is prone to avalanches (in fact, the party already encountered one). The party is attacked by a pair of trolls. The 9th level halfling rogue decides it might be worth trying to bring down some heavy rocks on one of the trolls. The rogue makes an Easy (DC:8) Nature check to find a precariously balanced group of rocks. He then makes a Moderate (DC:14) roll to hit them with his sling. Success will bring them down on the troll for 2d6+5 (Medium Normal) damage.
Obviously, this is just a handful of scenarios, but they showcase the usefulness and flexibility of the improvised damage system. They encourage creative thinking in players without unbalancing the game. So go ahead and give improvised damage a try. I think you will enjoy the results.