D&D 5E I think I am going to stop using solo monsters.

[Dualazi]

CR is sadly an almost entirely useless metric in 5e so this isn't a huge surprise, and obviously just about everyone has commented on the fact that you have 8 players which makes it even *more* useless. Even going by XP a marilith split 8 ways isn't overwhelming from an encounter planning standpoint, helped further by the fact that it was summoned into such a heavily prepped area, which would decrease its effective CR substantially. That this was only allowable due to two areas of handwavium (them planning in secret and being able to summon well before they're normally able) is, unfortunately, your fault as a DM.

If you want to run bosses/solos in 5e, I'd recommend reading up on some 4th edition mechanics as such to make them viable. Give them multiple turns, prodigious HP, legendary resistance, all that jazz. If you're using what is otherwise a non-boss creature (like the marilith) you're going to have to make a custom version of it, or give it a large number of minions to help.

 

[UngeheuerLich]

[MENTION=76140]Reinhard[/MENTION]
IF I would seach for a problem it would be the glyph of warding spell.
The trap was also foolproof. Even if the Marilith stood for 9 more rounds, the magic circle would have made sure she would eventually die. It is a death trap for deamons and meant to be that.

 

[unknowable]

@Reinhard
IF I would seach for a problem it would be the glyph of warding spell.
The trap was also foolproof. Even if the Marilith stood for 9 more rounds, the magic circle would have made sure she would eventually die. It is a death trap for deamons and meant to be that.

She would just teleport out of it. A CR 14 or 15 charisma save isn't that difficult to escape for something with a +10 to charisma. Random chance is always in play, but still.

1) The ability to actually summon the marilith was handwavium. In game story reasons provided the opportunity so the 5th level PCs could do it.

The cost associated that was given was also too low. And really, high level characters don't have that sort of power ready to summon high cr monsters against their will.
I would suggest opening planar gates in the future.
A Marilith against that party isn't a Deadly encounter as people have said before and as such will not come close to providing a challenging solo experience. Even without the party gaining advantages out the wazoo. (Sure the CR system is flawed, even for a party of 4... But this example is not a case where the CR system is the main issue. A perfect CR system couldn't account for this)

2) Related in game story reasons let the PCs plan the summoning in secret. This was a decision I made because I saw the CR 16 and said I should give them a little boost. I did not realize that little boost would make the encounter trivial.

Anything that gives a party a surprise round and the ability to plan it all out to extreme levels is going to essentially 2x-3x their output. This isn't necessarily bad, just be aware that it will happen.
Players should be rewarded for actual creativity, but unless you plan on running easy encounters they need to be balanced out against what you as the GM hand to them advantage wise.

3) They summed the marilith into a reversed magic circle where they had laid down 4 glyphs of warding, each of which cast 3rd level Cloud of Daggers in one of the 4 squares she occupied. So, she is summoned (surprised) and glyphs go off doing 24d4 magic slashing damage (no save or attack roll). On the start of her turn (she was the second in the initiative order) she takes another 24d4 and can now take reactions.

Obtaining 4 200gp valued diamonds should be fairly difficult under normal circumstances. It doesn't have to be, but it is a part of the spell's requirements. And I just realised this meant you allowed them to summon a specific high level demon without any actual cost. Ouch.

4) Various characters attack her in various ways, whittling her down a little (she parries some of these attacks).

Are the characters using rolled stats?
What magical items did you give them? (Curses should have some sort of actual negative effect btw, in this case with the planning grants you removed the negative effect entirely)
Why didn't the Marilith have her own magical artifacts in this case? (Iron flasks with some hellhounds would not have gone astray)
Did she teleport out of the circle? The save DC should have been easy for her to overcome.
How many magical items does the party have? The system is expecting 1 uncommon magic item per player at level 5 as per the DMG.
Identify doesn't reveal if an item is cursed and certainly not what cursed it.

5) At the start of her next turn she takes another 24d4 and dies before she can actually act.

Note that while Cloud of Daggers requires concentration, Glyph of Warding specifically states that concentration spells last for their full duration when cast through GoW, bypassing the concentration rules. Also note that the wizard PC player that set the trap is my go-to rules/optimization player when I need some insight into the fiddly bits of the system.

[/QUOTE]
I would also say that cloud of daggers would be resisted. It is a powerful spell even with resistances and the spell doesn't specify magic or elemental damage as other spells do.
But that is up to the GM and only came up in my game when some players were arguing about whether the catapult spell was making it's projectiles deal magic damage (RAW, for sure... RAI... ehhhh)

It should be fairly effective though, it uses up two level 3 slots per character casting it.

 

[pogre]

I wonder if the players actually enjoyed the encounter quite a bit. They were taking what they viewed as a sizable risk and made a solid plan. When the Marilith showed up the plan was executed to near perfection. High fives all around.

Now, I will grant you the OP D.M. seems disappointed with the result. However, sometimes players really relish steamrolling an encounter like this. Fun is fun.

If the players were disappointed that is more of an issue IMO.

 

[werecorpse]

I think your decision to stop using single monsters (I'm not using the term "solo" on purpose) in 5e against a party of 8 is sound thinking. The example of the Marilith was also a lot about preparation and the ability to nova which in D&D have always been key way to significantly boost the power of the PC's.

So the PC's had 3 advantages, single monster, known ability to nova, ability to prepare for the specific fight.

You can use a single monster against a large group of PC's but unless you grant it some sort of major defensive boost or action economy boost (or both) you have to go way up the CR table, although this is something contemplated by the DMG.

I run for a group of 7 PC's and they chased away a dragon recently - he only had one ally. It is slowly dawning on all the big nasty monsters in my world (through me) the important effects of the action economy. They will be taking in game steps to remedy this weakness. More bodyguards or the ability to negate actions against them - or both.

 

[Yunru]

I wouldn't say that nova ability only applies to DnD. There's a reason the Blitzkrieg got as far as it did (and the same reasoning for why it failed when it stalled).

 

[GameOgre]

I would have given it to them just like the OP did.

I mean they friggin summoned a Marilith! How cool is that? and had a great that a boy battle to! Heck yeah!

Now afterwards like 2 adventures latter I would start throwing massive almost overwhelming ambushes at them as Orcus or some other demon lord targeted them for termination! I mean come on they started a war with Hell itself!

Slap a curse on them, hound them with demons and devils. Maybe the most famous party member gets summoned by the demons! Turn about is fair play right? Have their families get killed off or become corrupted"Mom? Not you to mom? Noooooo!"

This is a DM's dream game.

 

[unknowable]

That is another point that is worth bringing up.

If players get used to you giving them out of system advantages when it comes to challenging combats they may feel cheated or harassed if you decide to play by the rules or play a monster smarter in the future.

 

[werecorpse]

I wouldn't say that nova ability only applies to DnD. There's a reason the Blitzkrieg got as far as it did (and the same reasoning for why it failed when it stalled).

Agreed, I didn't say it only applied to D&D - nor does the ability to prepare, nor having a major numerical advantage.

 

[Imaculata]

You just can't expect one Marilith to be much of a challenge when the party size is twice the normal size AND all the players are thoroughly prepared for the encounter AND they get a surprise round.

That pretty much negates the point of the CR entirely.

But regardless, it is always a good idea to have some backup for your boss monsters, and to make clever use of the terrain when setting up your encounters. If everyone can focus on the same foe and win, then obviously it's going to be easy. This is why I always give the players multiple goals.

I often return to this example from one of my campaigns:

The Forge Guardian

This powerful automaton was pretty much invincible, as long as four animated statues were still alive, which provided the Forge Guardian with buffs (damage reduction, miss chance, spell failure, regeneration). The Forge Guardian also controlled the terrain in which the players could fight him, by having an ability to pour molten steel into the arena. So the players were forced to divide their attention, and focus on multiple foes at the same time.