How do area effects stack?

[delta]

I'm looking for what most DMs might do when handling simultaneous, overlapping, harmful area effects. I'm thinking about stuff like:

• Dragon mates crossing breath-attacks
• Theurgists casting overlapping webs
• Ogre magi casting ice storms on the same place
• Mind flayers ambushing with overlapping mind blasts
• Gorgon herd breathing in the same place
• Medusa group all coming in sight at once
• Troglodyte tribe with a hundred members throwing stench

What is the best general policy for these situations?

[waysoftheearth]

The medusa group is similar to the carrier crawler with 8 tentacle attacks, any of them causing paralysis. Should the player save versus petrification (or paralysis in the case of the crawler) just once or several times?

If you prefer more abstract combat, then a single save is probably enough. The multiple areas, lines of sight, attacks, or whatever increase the coverage of the danger (potentially exposing more figures), but don't alter its intensity.

If you prefer more detailed combat, then you might be more inclined to dice for each individual medusa glare, crawler tentacle snap, or area effect weapon, with each attack having its own impact and saving throw.

I find myself leaning more toward the former as time goes by. Besides, survival of the D&D PC is challenging enough already!

[hamurai]

In case of non-lasting effects like dragon breath or mind blasts, they're all applied one by one. A combat round is 1 minute long and the breath attacks don't happen at the exact same time.

Several instances of lasting effects, like the stench of a group of enemies, only apply once, as they're not distinguishable - you won't smell the enemies one after the other, unless one stays out of reach and comes in later.