Making a Troll Boss

[Aergentum]

Hi there. For my campaign I'm having issues on making a good final boss and I need some advice on it.

The party is a 6 member party of 7th level: Barbarian, Glamour Bard, Hunter Ranger, Aracane Trickster Rogue, Shadow Monk and Draconic Sorcerer.

Thay are now investigating in some old caves that are somehow connected to an old dwarven settlement. Now the Trolls have made this palce their home and the party needs to drive them out.

They already waltzed trough a pack of 8 Trolls that were guarding the caves, and now are en route to fight the boss. They have seen him before, but I made him run away with other trolls, because I feared that they just might kill him too quickly.
The party is pretty good, but I want this fight to be risky for them and not just another fight encounter.

So far this is what I thought the boss should be:

Boss Troll

HP: 280
AC: 18 (Worn Armor)
Features: Pack Tactics, Multiattack (3 attacks), Improved Regeneration (20 HP)

He should fight with three Trolls at his side.

What do you think? Would this be too weak/hard for a 6 party member group?

[Zhorn]

I threw a vemon troll at my players a couple of weeks back (MToF), and that splash damage to everyone in melee range made for some very interesting decision making (especially when someone's at low HP nearby).

Having one of those guys pick up and carry one of the players once they knock them unconscious will put everyone in a panic, especially if they start to flee. Sure they can attack it at range to try and stop it, but those venom splashes are an auto hit, and those failed death saves can pile up fast if the party isn't careful.

[hymer]

That Boss + 3 trolls should be easier than eight trolls according to a quick encounter calculation.

[redwizard007]

Add some lair actions to gain parity with action economy.

Activate traps (falling boulders or logs.)
A portcullis falling and splitting the party on round 1.
Stomping on a fire to reduce light/increase smoke.
Raging like a barbarian (resistance is a big deal.)
Calling for reinforcements that arrive next round.

Of course, none of those actually have to be "lair actions." They can just happen.

You could also include some terrain issues.

Winding, narrow tunnels that reduce line of sight and only allow 1 or 2 PCs to engage the troll at a time.

A deep pool of water that gives advantage or resistance vs fire.

A waterfall. Everything is coated in water (athletics to not fall if damaged,) and a mist both grants disadvantage to attacks (poor sight) and further impedes fire attacks.

Boulders that the troll can throw/roll at PCs for significant damage.

Stalagmites that grant cover.

Pair the troll with another creature that has different weaknesses.

[Randomthom]

Something environmental that doesn't affect the trolls could add to the encounter difficulty and spice it up a bit.

He could live in a slimy pit (Dex save or fall prone when moving a la the Grease spell). You could even have the slime start just before his actual lair on a downward slope towards a pit of spikes. Perhaps adjudicate that the rough feet of the trolls seems to not be similarly affected.

Perhaps he will also be wearing a ring of fire resistance (or his makeshift armour is Leather armour of fire resistance?) so even though it prevents his regeneration, he takes reduced damage. Powerful items to give your players afterwards though...

Also fun, give the troll boss a few pet Rust Monsters that he treats like a pack of dogs. Finally... how about a Troll Shaman ally/lackey with a few Druid spells?

[darknite]

You know your group. What do you think?

Groups normally hit a little higher than you think they can when you push them. One thing you can do is make it very tough but have some pressure release mechanisms if things start to go very obviously wrong. Perhaps one of the Troll's bodyguards is deathly afraid of fire and attacks at disadvantage once they've taken fire damage. Perhaps the boss has got a hangover from powerful troll grog and has to roll 4 attacks for Multiattack and take the lowest three results. Etc.

[Unoriginal]

I would up the mental stats of the boss a bit.

Not only it's appropriate for a leader, it also make them a bit more difficult to hinder or harm with spells.

[darknite]

I would up the mental stats of the boss a bit.

Not only it's appropriate for a leader, it also make them a bit more difficult to hinder or harm with spells.

I like that. Maybe a couple of Indomitables to keep them from rolling over to the first spell that hits them?

[Sparky McDibben]

Maybe give them a legendary resistance to resist a save or suck.

But also, have the lair be flooded with natural gas so if the PCs try to use fire - boom!

Maybe have one of the trolls be either a venom or rot troll from MToF. It adds some variety. Or just give a regular troll the following:

When this creature takes damage, its venomous blood splashes onto anyone within 5 feet, dealing 5 (1d10) poison damage.

[Vogie]

I'd make it a two-phase fight, like a MMO Boss with an Enrage condition. That allows the first half of the fight to act as normal, but when you reach a threshold trigger, it changes.
This second phase of the fight may include:

The actual Rage mechanic
A Leadership ability (concentration-less Bless)
Releasing a single giant riding beast, like a triceratops from a cage
Summoning a pack of hunting animals, like dire wolves or giant hyenas

The threshold trigger could be

Reducing the Boss Troll to Half Health
Killing all of the little trolls
Setting the Boss Troll on Fire for X rounds


You could also use different aspects of it. Perhaps you have one or more of the Trolls have the optional Loathsome Limbs trait, or maybe the boss troll speaks dark magiks after the party kills the 3 little trolls, and their limbs come to life.

[Aergentum]

Thanks to all for the suggestions.

The two phase battle is intriguing and also some environmental hazards and covers is nice. The battle is settled in his lair after all, so I would have set up at least some traps.
I'll brainstorm a bit about the possible traps or tricks on the lair.

About the "Rage" it defenitely fits this kind of boss, and would be a fair fight with the Barbarian and the Ranger. Probably I'll also spec up the mobs that accompany him (like they are his personal guards).