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View Full Version : D&D 5e/Next Traps: Levelled DCs and Balancing for Encounters



Iituem
2017-08-22, 04:27 AM
The Tables, for Quick Reference.



Lethality
Trap DC
Save DC
Trap Attack
Trap Damage
Trap Rating (TR)


CR 1-5







Setback
11
11
+4
1d10
1


Dangerous
13
13
+7
2d10
3


Deadly
17
17
+10
4d10
12


CR 6-10







Setback
13
13
+7
4d10
1


Dangerous
15
15
+7
6d10
2.5


Deadly
19
19
+10
10d10
8


CR 11-15







Setback
19
16
9
6d10
1


Dangerous
22
17
+10
10d10
2.5


Deadly
27
19
+12
18d10
8


CR 16-20







Setback
21
17
+11
10d10
1


Dangerous
24
18
+12
18d10
3


Deadly
29
20
+14
24d10
8


NB: TR values are for 'full party' damage. Divide by 4 for a 'single target' trap.
Total TR for an 'average' CR encounter for that band is 14. [i.e. CR 3, CR 7, CR 13 and CR 17.] +3 or -3 for each 'step' above or below. Use your judgement. An encounter should average 5-6 traps, but again, use your judgement.


So, I recently decided to run a heist adventure for my party based around stealing the Merryweather Falcon. A major part of the break-in was overcoming the various traps and defences of the Gilthammer Forge (elite dwarven jewellers for victory!), enough that I really wanted to run the traps as their own series of encounters without having to rely too much on monsters and NPCs. Guards were there, but it's a stealth-focused party and they get a lot of mileage out of not starting a fight in the first place.

I ran into a couple of problems here. First of all; are the Trap DCs in the DMG entirely appropriate for my 8th level party? Second of all; how many traps are appropriate for my party as an encounter? How deadly? Thirdly; how much XP do I assign at the end of the day?

The answer that many DMs will give you for the third is, of course, "eyeball it" and give them what you think is fair. Which is entirely reasonable. But some of us grew up under 3rd Edition and we like having guidelines for encounter XP.

Above, then, you will find my personal tables for Traps based on party level 'band'. This has been based on the DMG table (http://5e.d20srd.org/srd/traps.htm#trapEffects), tweaked to be a little more challenging, a little more balanced. Spoilered below is the rambling analysis I did when I built this table, which is included in its original and chaotic form for those interested, but I have included a neater explanation as well.


Explanation of the Table:

- I have separated Trap DC and Save DC for the higher levels. "Trap DC" is both the Investigation DC to find the trap and the Thieves' Tools DC to safely disable it. Save DC is the actual saving throw players need to make to avoid or halve (depending on the trap) damage or other consequences.

- I have included a new stat, Trap Rating (TR). I found that 14 'Setbacks' were about the equivalent in terms of damage dealt and resources expended for a CR3 encounter for a Level 3 party. The higher TR values are based on how much "Fun" a trap provides as a measure against both the Setback baseline and the total amount of trapping for an 'encounter'. I find from play that 14 Setbacks is way too many rolls, but 2 Deadlies is way too much damage and too little fun, so the traps work best mixed and matched. The TR values assume that the trap deals damage to the entire party (e.g. crushing room trap, poison gas). If the trap only targets a single character, divide the TR by 4 for that trap.

- XP rewards should be the same as for an encounter of the same CR.


How I got to these weird numbers:

- Monsters vs Party Stats. I found that the stats of a CR 3 monster (as laid out in the DMG's monster building guide) was roughly equivalent (or just sub-par) to the theoretical stats of a 4-man Level 3 party.

- CR 3 monster: AC 13, 107hp, +4 attack, 24 damage per round, Save DC 13.
- Level 3 Party Member: AC16, 18hp, +4 attack, 7 damage per round. The hypothetical 3rd level Fighter.
- 4x Level 3 Party: AC 16, 72hp, +4 attack, 28 damage per round.

As a rule of thumb, I went with a (reasonable) assumption that access to healing (by cleric or potion) increases a party's effective hp by half. So the Level 3 party has 108hp, leaving them almost exactly the same as the theoretical monster. It is my assumption in this calculation that the penalties and abilities of other classes essentially even out to this average Fighter 3 character (Lower AC? More damage per round, etc.).

As displayed in the rambling original section, I based my Trap TRs on the idea that they do a proportion of the hypothetical CR 3 (or higher) monster's damage to the party over its whole encounter and therefore require expenditure of party resources (spells, potions etc). Skipping the elaborate maths, they come out as follows.

- A Setback should consume around 6% of a party's total hp.
- A Dangerous trap should consume around 15-20% of a party's total hp.
- A Deadly trap should consume 50% of a party's total hp, potentially KOing weak party members.


Anyway, that's all the explanation that I think merits anyone with a normal attention span. For my absurd full calculations, see below.

CR 1-5: A typical level 3 player (Ftr) can be assumed to have a primary ability score of 15-16 (+2/+3), and a proficiency bonus of +2. If they go with a standard weapon (d8) and a shield, they can be expected to do an average of 7 points of damage per round, with an average attack rating of 14. Assume an average of 16 AC (Chain and 2 Dex, plus a Shield) and around 18 hit points. Since character with less hp tend to have bonus damage, healing or damage/support spells it evens out fairly well.

CR 6-10: Level 7, (Ftr again, for ease), the player's primary ability has risen to 17-18, we'll go for the +4 because magic items can help. Their Prof bonus has risen to +3. They now do 2 attacks per round, averaging out at 18 damage, with an average attack of 17. Special abilities count for an extra half attack, which they will have at least 1 of, so call it 27 damage. AC may have risen to 17 because of magic items, they have around 36hp, but healing realistically increases that by half now, to around 54.

CR 11-15: Level 13 (Ftr, for ease), the player can expect to have their primary at 20, thanks to levelling or magic items, so +5. Prof is +5 as well. 3 attacks per round, and abilities make it an equivalent of four, averaging out at 11 per attack (+1 from magic weapons), 44 total, average attack of 20-21. AC can be expected to be 19 by now because of magic items. 78 hp halved up from healing makes 117hp.

CR16-20: Level 18 (Ftr), Capstone feature and lots of modifier bonuses. Primary at 20 for sure, with secondaries raised.. +5, with +6 Prof. 3 attacks per round, abilities push that up to 5, call it 14 per attack (+2 magic weapon and some extra bonus or other) to 70 total, attack average 23. AC has risen up to 21. 162hp after healing.


But what does this mean in terms of balancing encounters? The DMG suggests that an appropriate CR3 monster is as follows:
AC13, 107hp, +4 attack, 24 damage, Save DC 13.
Compare this to the Level 3 player:
AC16, 18hp, +4 attack, 7 damage (Save DC will vary, for primary casters 14-15, but then it replaces attack.)
If we multiply damage and hp by 4 to account for the classic 4 man party, this becomes:
AC16, 72hp, +4 attack, 28 damage. The hp raises to 108 if healing is in effect as with later levels.

In effect, you want the challenge to be about equal to the nominal 4 man party's stats (although the party has slightly higher AC and damage because they're the PCs).

So let's think about this in terms of damage. The players hit the monster 55% of the time, averaging out at 15.4 damage per turn. The monster hits the players 40% of the time, averaging at 9.6 damage per turn. Granularity means these figures will rarely turn out this neatly, but it's a fun idea.

Deadly: Trap DC 27. Save DC 19 / Attack +12. 18d10 damage on hit.
Therefore, the players will usually have about 7 exchanges with the beast before overcoming it (or the beast winning in 11 rounds). This is an idealised combat with a powerful, hp heavy low AC beast such as some sort of ideal hill giant.

What does this mean for trap encounters? Well, the DMG gives the following stats for traps of level 1-5:
Setback DC: 10-11. Attack: +3-5 Severity: 1d10 damage (6).
Dangerous DC: 12-15. Attack: +6-8 Severity: 2d10 damage (12).
Deadly DC: 16-20. Attack: +9-12 Severity: 4d10 damage (24).

In a sense, then Attack traps have the following odds vs a Level 3 party:
Setback: +4 (40% hit rate), 6 damage. Averages 2.4 damage singular, or if it's a whole party hit 9.6.
Dangerous: +7 (55% hit rate), 12 damage. Avg: 6.6 singular, 26.4 party.
Deadly: +10 (70% hit rate), 24 damage. Avg: 16.8 singular, 67.2 party.

Saving Throws traps (most characters will have their primary stat not be the Saving Throw stat, so call it +2 to saves.)
Setback: DC11 (45% hit rate), damage as above.
Dangerous: DC 13 (55% hit rate), damage as above.
Deadly: DC 17 (75% hit rate), damage as above.

In terms of damage output, therefore, a whole-party Setback is equivalent to one round of attacks from the CR3 monster. A single Dangerous attack is about 2/3rds that, while the full party attack is equal to 2.75 rounds of attack. A single dangerous attack is worth 1.75 rounds of attack, while the full party is worth 7 whole rounds of attack. Given the average party hp is 18, it usually isn't enough to kill a character outright in one shot, but it is enough to drop them.

As we saw above, 7 rounds is a fair estimate of the 'ideal' encounter length between a CR 3 creature and a level 3 party. It might therefore be tempting to think that we can count a Deadly trap as equal to the CR 3 monster. But it isn't that straightforward.

In fighting off the monster, our level 3 party will end up making around 30 rolls, mostly attack rolls with some saving throws thrown in. They will expend healing potions for the weaker party members, or have to take a short rest afterwards to recoup health. Spell slots will be expended for dramatic damage.

In facing the Deadly trap, our party makes between 2-7 rolls: 1 roll to Investigate the trap and find it; 1 Tools check to disable it; and if either of those fail 4 saving throws (or the trap makes 4 attack rolls). They might have to expend potions if they fail, but it only costs 1 spell slot, perhaps, to disable the trap, or even none if the rogue can do it all safely.

In fact, assume that a Rogue is doing the Investigation and Trap-Disarming. For our CR 3 group, that means a bonus of +6 to the checks (+2 Int, +2 Prof, +2 Expertise). The odds then go as follows:
Setback: Spotted (75% chance), Disabled (75% chance), Activated (43.75% chance; 45% hit rate) - Avg Dam: 1.2 / 4.8
Dangerous: Spotted (65%), Disabled (65%), Activated (57.75%; 55% hit) - Avg Dam: 3.8 / 15.2
Deadly: Spotted (45%), Disabled (45%), Activated (79.75%; 75% hit) - Avg Dam: 14.4 / 57.6

If we assume that it averages at about 3 rolls per non-Deadly trap, then 10 Setbacks do 12/48 damage, 10 Dangerous do 38/152 damage. The beast will have done around 67 damage over 7 rounds, so we can about average that by doing 3 party damage Dangerous encounters and 5 party damage Setbacks.

Note that Setbacks drop 6.7% of party health at a time. They are a sapping measure, compared to the 21% of Dangerous traps and the 80% blast of Deadlies.

So let's say that to do 67 damage takes 14 Setbacks. Making 1 Dangerous worth 3 Setbacks. 1 Deadly would be worth 12 Setbacks, but discouraged from overuse. [Setback: 1 TR. Dangerous: 3 TR. Deadly: 12TR. 1/4 TR for single target.]

So, my recommendation is that an encounter should have at least 4 traps, worth 14 Trap Rating at CR3.


Alright, let's look at the CR6-10 lot. Party has:
AC 17, 216hp, +7 Attack, 108 damage. Rogue Checks: 20. Avg Saving throw: 14.

Setback: +4 (35% hit chance), 12 damage; 4.2 single damage, 16.8 party damage
Dangerous: +7 (50% hit), 24 damage; 12 single damage, 48 party damage
Deadly: +10 (65% hit), 60 damage; 39 single, 156 party.

Since Discovery/Disable DCs remain the same, it makes Activation chances:
Setback: (9.75% Activation: 35% hit rate); Avg Dam: 0.41 / 1.64 Setbacks are no longer a threat.
Dangerous: (27.25% Activation; 50% hit); Avg Dam: 3.3 / 13.2 Minor danger. Now the true Setbacks.
Deadly: (49% Activation; 65% hit); Avg Dam: 19.5 / 78 Just over 1/3 of party health.

Setbacks no longer do appreciable damage even when they hit. For a level 3 player, it was 1/3 of full hp, perhaps 1/5 of realistic hp when you account for healing. Now it's 1/10th if that. The Dangerous hit, by comparison, when it springs, does 20% of a party's realistic hp. That makes it equivalent to the earlier Setback (but beware; only 13.2 damage on average makes it 6% of party health, back to true Setback levels).

Let's say we keep the earlier Dangerous stats and make them Setbacks now. The new Dangerous assumes the same damage but takes a DC of 15 to bypass.
Dangerous: (44% Activation; 50% hit); Avg Dam: 5.3 / 21.2
That's a little spicier. Effective damage is upped to 10% of party health. Still, though, that's not too much. Let's add in some more damage dice and make if 6d10, for the following:
Dangerous: (44% Activation; 50% hit); 7.9 / 31.6
That's better! Still a good chance of avoiding it, but does 15% of party health instead. Now we're closer to the old Dangerous levels; it's enough to be a serious inconvenience. But what about Deadly?
Deadly as it is does about 1/3 of party health, which is nice, but we want something that does more like 50%. If it always went off against all the party it would do 156 party damage, or 72%. So we want about a 70% activation chance. That puts us at a DC of 19; a 55% chance of success for our +10 Rogue. Resulting in:
Deadly: (70% Activation; 65% hit); 27.3 / 109
Which is damned near exactly 50%. That gives us a Trap bracket for Level 6-10 of:

Setback DC 13 / Attack +7. 4d10 damage on hit.

Deadly DC 19 / Attack +10. 10d10 damage on hit.

Remember that single target traps are worth 1/4 of party traps. Since our goal is to punish perhaps 85% of the party's total hitpoints for an equal CR, for our ideal CR7 encounter we want 14 TR as before with Setbacks worth 1TR, Dangerous worth 2.5 TR, and Deadly worth 8 TR.


CR11-15 Time! Party has:
AC 19, 468hp, +10 Attack, 176 damage. Rogue Checks: 25. Avg Saving throw: 16.

I can sense a pattern here, so let's go ahead and make some suggestions.

Setback: Trap DC: 19, Save DC 16 / Attack +9. 6d10 damage on hit.
Hits 50% of the time, 36 damage; 18 single damage / 72 party damage.
Activation Chance: 28%. Avg. Damage: 6.5 / 26

That makes for just under 6% damage, on par with our usual Setback levels.

Dangerous: Trap DC: 22. Save DC 17 / Attack +10. 10d10 damage on hit.
HIts 55% of the time, 60 damage; 33 / 132
Activation 58%. Avg Dmg: 19 / 76

16% of total damage. Back in line with the previous one, so I'm happy here.

Deadly: Trap DC 27. Save DC 19 / Attack +12. 18d10 damage on hit.
Hits 65% of the time, 108 damage; 70 / 280
Activation 84%. Avg Dmg: 59 / 236

Which is close as damn it 50% again. I reckon with that we can even keep the TR values from before.


And the final level, CR 16-20! Party has:
AC 21, 648hp, +13 Attack, 280 damage. Rogue Checks: 27. Avg Saving throw: 17.

We're close to the cap, so here are my suggestions.

Setback: Trap DC: 21, Save DC 17 / Attack +11. 10d10 damage on hit.
Hits 50% of the time, 60 damage; 30 single damage / 120 party damage.
Activation Chance: 36%. Avg. Damage: 11.7 / 43.2

Just over 6%, we're good here.

Dangerous: Trap DC: 24. Save DC 18 / Attack +12. 18d10 damage on hit.
HIts 55% of the time, 108 damage; 59 / 236
Activation 58%. Avg Dmg: 34 / 136

20% of damage, but they're good at recovering by this point.

Deadly: Trap DC 29. Save DC 20 / Attack +14. 24d10 damage on hit.
Hits 65% of the time, 144 damage; 93.6 / 374
Activation 84%. Avg Dmg: 78.6 / 314

48%, which is close as I care to tweak.

Final TRs are: Setbacks TR 1, Dangerous TR 3, Deadly TR8. Have fun!