Ignored troops? Interesting. No specifics, just that they ignored them. So none of their attacks were effective? Four DC 14 Con saves and no one was stunned? No one was poisoned by spores? No attacks hit at all?
The archer ignored the troops and the ranged Eldritch Blast devilsight guy.
The party could only see 120', but the Marilith didn't move back 40' or 80' to be 160' or 200' away while her troops closed in? Then she could pop back in with her 120 teleport in addition to her 40' move.
No. She was leading the band and had been crushing humanoids. She decided to move forward to attack with her troops.
"A few banishment spells"? As in the 4th level spell? That is a considerable expenditure of resources for 10th level casters. Of course this was probably the only encounter for the day, right?
Two fifth level spells and a 4th level spell. The party is six members. They have 6 fifth level spells and 9 4th level spells. Three spells eliminated four targets fairly quickly thinning the group. They still had 4 5th level spells and 8 4th level spells.
And the marilith didn't have any scouts out? Quasits are CR1 and can be invisible all day. Why wouldn't she have any with her? Have a few quasits find the party and report back. Have a couple Hezrou round a corner in front of the PCs. When they attack they "realize" they are out gunned and run away around a corner or something (or are corners unusual environments?). When the party gives chase they are ambushed by the rest of the warband. If the party doesn't give chase just wait to attack them when they sleep. Or really anytime when they can get close without a 120' featureless kill zone between them and the party.
She had six Shadow Demon scouts out. The party spotted them. They ran. The party moved back in the other direction, hid, and ambushed the shadow demons using
pass without trace. It's very hard to ambush groups with players with high Wisdom, the Observation feat, and double proficiency bonus on their Perception. Have all of those things in the group, it's extremely hard to ambush them. Most of the group is drow and one Devilsight player with 120 foot darkvision. So they can match what the opponent can see. Even invisibility is not a guarantee of success against them. If they hear something, they will cast
see invisibility and annihilate it.
This is something I find strange as well. Do you not play with characters that build to notice things? Every single party I've played with has had double proficiency bonus Stealthy scouts and double proficiency bonus Perception. Every one of them. If I want them to not notice something, I have to make it up. Which I've started doing on occasion. This adventure is about testing demons out of the book to see how they do. I'll start modifying them after I get a feel for them.
And why where they attacking a hard to hit Bladesinger? Are you really telling me that 15 demons were unable to close on any spell caster at all? Or the sharpshooter archer? Really?
Because he was running by them provoking AoOs from them and does substantial damage with his whip. If someone was hitting you for a bunch of damage, might you not try to attack him? The bladesinger is a paladin2 /bladesinger 8. So he has a lot of smites and Booming Blade is surprisingly effective with a whip. That was an interesting tactic to see given I didn't think much of Booming Blade or the Bladesinger class. My eyes have been opened.
They closed on them after the marilith was dead. They did some damage. At that point it was, meh damage in my opinion. Chasme don't have great hit rolls so a few
shield spells.
So the master tactical genius Marilith charged the party in a strait line while taking fire. Even then they should all close on the party in two rounds even with the party retreating as they fired. They took out 15 demons in two rounds? With bounded accuracy there is no way that every character in the party had ACs so high that none of the demons could hit them.
The master tactical genius went forward with her demons in front of her looking to do some damage. They were providing her with cover as she closed. She figured she could leave with her
teleport. So I'll give you an exact sequence.
The cleric cast
bless on the paladin/warlock, paladin/bladesinger, and ranger/fighter (Notice lots of multiclassing and paladins...we might have to try a campaign without multiclassing). So the opening round the archer beats the Marilith on initiative and the cleric beats the sharpshooter (due to the Alertness feat, he has a high initiative modifier).
So the Sharpshooter with his magic bow (+2 bow) and
bless fires all attacks at the marilith. He moves forward 30 feet to
hunter's mark. We are using Unearthed Arcana material. So he has Close Quarters Combat and Archery Style (fighter/ranger) and is a Deep Stalekr ranger (1 extra attack on the first round of combat). He Action Surges and unloads five Sharpshooter arrows at her. Attack bonus +4 prof +5 dex +2 bow +1 Close quarters fighting +2 archery style -5 sharpshooter +1d4
bless. Each attack is +9 +1d4. He hits four of five attacks. He does 1d8+1d6+17 per attack. So he did 100 or so in round one of her 180 points. As you know cover and distance don't much matter to a Sharpshooter.
She was pretty much neutered in the opening round. 80 hit points against a six man party is absolutely nothing and will disappear quite quickly. I could have had her run and leave. That was the only way she was going to survive. I figured she would want to try to and hammer a character, so she advanced teleporting to the archer. And she did some damage to him and he had to use a
shield spell. He's a ranger/fighter Eldritch Knight. But by round two she took hits from the warlock/paladin/sorcerer using
eldritch blast[/.I] with hex. The bladesinger smote her a couple of times with his whip. I think the archer hammered her with two attacks only hitting with one that round. She was down to 10 hit points by round 3 or some trivial amount. I figured she knew she was heading back to the Abyss and decided to go out swinging.
After she was dead, the other creatures were cleaned up. They did some damage. Maybe one or two players missed a sickness save for a round from the hezrou. Almost my whole group has good Con saves and big bonuses from the two paladin auras.
You see? This is why those like myself find it hard to believe that you can't challenge a high level party. Even if they are "optimized".
I find it hard to believe you're having an easy time challenging an optimized party. My players are using multiclass plentifully. Charisma-based classes synergize in an amazing fashion in 5E. The weak classes are strength-based classes and my players avoid them. Barbarians and non-magic using melee fighters are avoided. Non-magic using rogues are avoided. Strong feats are Resilient Con, Sharpshooter, and at least one character with Alertness or Observation. Expertise is used for Perception and Stealth for scouting. You ensure you have these things in you're group and you maintain a power advantage over the enemy that is nearly insurmountable.
Your chances of ambushing them are minimal. They have consistently high damage with abilities like eldritch blast and Sharpshooter while having powerful nova abilities with the paladin multiclassers. I have three paladin multiclasses in this group. The main complaint I'm getting at the moment from my players is that they feel like they're playing the same classes over and over again. I tell them, "You are." The power band is very narrow in 5E and they have already determined the power abilities and the power tactics in 5E. They have determined what to avoid like being in melee too much. In a game where mobile ranged attacking is by default amazing, they tend to avoid meleeing.
As a DM I can match their capabilities here and there, and that is what I do, but stuff out of the box doesn't work very well. I need to modify it to deal with the capabilities of the party. I'll do it more now that I've had some time to see higher level 5E in action from the DM side. I'm seeing all the problem abilities in these first two high level campaigns. I'll run this one to 20 with boons. I'm building my house rules document right now to adjust some things. Sharpshooter is the main feat I'm reducing.
The fight was the second fight of the day. The first one was the six shadow demon scouts they ambushed. That didn't use up much resources. They are traveling right now. So they only get a few encounters a day. Soon they'll be walking into Baphomet's maze. I've taken some measures to limit resource recovery, so they have to preserve more than they've been doing. Though they still aren't using much in terms of resources due.
Let me see if I can remember. In that deadly fight, they used:
2 5th level banishes
1 4th level banish
1 1st level bless
1 3rd level haste with 3 sorcery points to twin it (cast on bladesinger and sharpshooter)
1 1st level hunter's mark (I think this dropped after he was attacked by the marilth)
1 1st level hex warlock slot
I don't think they cast much else. Just absorbed the hit points, fell back down the tunnel to a relatively safe location, and took a short rest to recover some hit points at a safe location after defeating the warband.
Don't get me wrong. They took some damage. More than a few characters lost half their hit points by the end of the fight. The marilith wasn't as interesting as the 3E/Pathfinder marilith tactically. The lack of spellcasting to support her demonic troops really made her limited. Sure, she could have fell back and waited for the party to use resources thinning her group, but the result would have been the same with six players unloading on her. That wouldn't have went any better than one unloading everything on her in round 1. 180 hit points to 5E characters is not much. If you don't have ranged capabilities against a party that can see you 120 feet away, you don't have much you can do.
The Pathfinder marilith could blade barrier, telekinesis, project image, fly, and had an unholy aura that substantially boosted her defenses. The 5E marilith has none of this. Just one teleport that takes her action. Her tactical capabilities are vastly inferior to the 3E marilith, yet the PCs tactical abilities are not reduced by the same margin. Why is the 5E marilith just a melee monster? Who made that decision?