View Full Version : [4e] Multiple Wave Encounters (DM)

2009-07-03, 03:22 PM
This is a trick to balance multiple wave encounters -- where you don't intend to give the party a break.

Suppose you want a multiple wave encounter of difficulty level X, and W waves.

Take X and add (W-1). Divide this XP budget into W parcels (roughly evenly).

To figure out the default delay between waves, give them roughly (5 * (level of wave+3))/(party level+3) rounds to mop up the wave.

Naturally, use monsters close in level to the party for the monsters in the wave, not the level of the wave.

If you want uneven waves, you can take a bunch of waves and turn them into a "wave of waves".

A level 2 party fighting a level 5 two-wave encounter. Each encounter is half of a level 6 encounter, or 125 XP each -- a level 2 encounter. You give them (5*5)/5 = 5.0 rounds to clear up the first wave before the second arrives.

You have a party of level 10 characters, and you want to throw a level 14 encounter at them. It consists of waves of cultists, followed by a demon (and possibly attendants).

The Demon is a boss fight -- so you want it to be half of the challenge of the encounter. So you split the encounter into two bits -- a boss fight, and a wave of wave of cultists.

Boss fight is half of a level 15 encounter, or a level 11 encounter (2400 XP).

The wave of waves is 3 waves that make up a level 11 encounter together, or 1/3 the XP of a level 13 encounter (4000/3 = 1333 XP each).

Each of the sub-waves is a level 6 encounter, which the party should be able to clear in about (5*9)/13 =~ 3.5 rounds.

Using 6 minions per normal mob ratio (4:1 is too weak for melee minions), we make the following waves:
Level 10 Ritualist (500) and 12 Level 9 (800) minions.
3 round delay
3 level 9 (400*3) Guards and 2 level 9 Minions (133) arrive from a back room.
4 round delay
Level 11 (600) and Level 12 (700) cabalists arrive -- maybe by teleportation.
4 round delay
Level 12 elite demon (1400), 8 level 13 minions (1067) appear in the summoning circle.

Total XP is 6400 -- or a level 15.5 encounter. Yet I think a party of level 10s would be able to survive, as it would be more like a level 14 encounter in difficulty.

Now that demon fight is rather extreme, and it is quite possible my math will have broken down by that point...

Math that justifies the above:

The basic idea is that the XP curve is non-linear.

6 monsters being fought one at a time is about 3.5 times weaker than 6 monsters being fought all at once, in terms of what damage they can do to you.

In essence, N monsters ganging up multiplies XP by 6, but danger by about N^1.7.

As it happens, the XP curve is about 100 * 2^((L-1)/4), = 84 * 1.19^L. This is only important locally, because we don't use encounters that are far away from the local XP area.

We then use the non-linearity of the XP values to emulate the 'rolling back' the gang-up bonus of swarms of monsters.

Bah, I cannot replicate the crunch I did earlier. There could be an error in the above derivation. I'll get back to it.

It appears that if I did an error in the 2-split case, it was in favor of the players.

Meanwhile, if anyone is brave, try out the above. :)

2009-07-03, 03:46 PM
I like your solution for fitting it all into one encounter, but you may not need to. What I did in a one-off adventure where I didn't want pauses in the story, is just say "okay, encounter's over". They recharge encounter powers, get the chance to heal themselves as if they had taken a short rest, and etc. It's a bit blunt, but it worked well enough.

If this works well, then I may like it better. My fear is that the initial waves may be torn down easily, and the final ones may become extremely difficult. Well, I suppose that's not "my fear". "My fear", as it were, is that this situation may be inevitable. Certainly it may be exactly what you want at times, but I'm wondering if it's possible to make all of the waves equally difficult. Slowly ramp down the difficulty as you go through, starting high? I'm not sure, I guess playtesting is the best way to find out for sure.

I'd also be concerned about how the structure of each wave works. Encounter design is easily as important as monster selection, and that may be thrown off when they're separated and forced to attack at different times.

While it is (of course) not yet proven, this is certainly an impressive system you devised. I'd be interested in trying it out sometime.