by Mike Shea on 30 October 2011
We DMs have a lot of things to balance when building encounters. We want mechanics that are fun for our players and fun for us. We want mechanics that keep the threat of a battle high. We want mechanics that fit the story we want to tell. We want mechanics that won't be too complicated.
Auto-damage effects are one such mechanic. It's not perfect and it's not something you'll want to use everywhere, but its a nice tool to have once in a while. Today we'll look at some auto-damage effects to see what advantages they hold and when best to use them.
Your group enters a huge chamber with a massive fiery cauldron in its center. A powerful wizard conjures fire elementals from this cauldron and sends them against the party. As the combat ensues, the cauldron bubbles and boils over, spraying lava in all directions.
Flaming Cauldron: At the beginning of its turn, any creature within 5 squares of the cauldron takes 10 fire damage per tier.
This is a pretty simple environmental effect and a good example of the advantages of an auto-damaging effect. It doesn't take up an initiative action. It simply activates at the beginning of a character's turn. Because of this, it also scales with the number of PCs in the room. If you have four PCs, it does less overall damage. If you have six, it does more. You also don't need to roll an attack or damage roll which means the cauldron doesn't slow down the battle. The cauldron is a big set-piece, but it doesn't need to be complicated. Your wizard and fire elementals will act more like traditional monsters. The cauldron just spews fire. It also does a consistent amount of damage regardless of PC abilities. This lets you set the challenge where you want it regardless of the PCs abilities or equipment. Only fire resist would limit this effect and that's fine.
You can do the same for traps as well. Instead of a dart trap that fires on an initiative with an attack and damage roll, you can replace it with a larger dart-trapped hallway.
Dart trapped hallway: At the beginning of its turn, any creature within the hallway takes level + 8 damage and ongoing 10 poison damage per tier.
Again we have a nice simple trapped area that we can place in the middle of a larger encounter. This isn't interesting enough to run as a central set piece, but if you have a larger encounter with one particularly hallway you want to spice up, this is a good way to spice it up without making the rest of the battle too complicated.
Auto-damage isn't perfect. It bypasses all the fancy gear and powers the PCs have, which isn't something you want to do often. It works best as a small effect you want to add to a battle already full of cool monsters. If you want a trap or hazard to be the central piece of a story, one with an initiative slot, an attack roll, and a damage roll is probably a better fit.