LF Advice - An appropriate Challenge for my party? (DM new to 5e)

[rahimka]

CONTEXT:
I'm a somewhat experienced DM, but pretty new to 5e, with a large party of fairly new players:
Goliath Fighter (Defensive-style, Champion path; the only experienced player)
Dwarf Druid (Shepherd path; very new player who is getting used to what she can do with her powerful class)
Elven Rogue (Thief)
Dragonborn Rogue (Assassin)
Half-Elf Ranger (Revised version, Hunter conclave, Archer)
Half-Elf Warlock (Hexblade, DMPC; token evil teammate, mostly hangs back in combat using his cantrips, tries not to show off how dangerous he can REALLY be in case he has to fight the rest of the party later...)

They are currently lvl4, and making their way from the rural villages and small towns towards the Capital City, taking on random encounters (like being ambushed by a jerk of a Paladin who they beat to the holy relic in a dungeon) and a few small side-quests/single-session adventures along the way (next up is the shady carnival in "No Foolish Matter"). But I want to throw them a REAL CHALLENGE before they get there. Something that will give them some cred as up-and-coming adventurers with folks in the setting who hear about it (like the international Adventurer's Guild, or the folks at the Mage College who the party will be trying to get info from when they get to the city)

What I have in mind: the party is finally reaching the heart of the kingdom, when they arrive at a large town only a few days upriver from the Capital. But danger rears its head when they discover the Lizardfolk of the nearby swamp have suddenly become very aggressive (either ambushing the party ahead of time, or in the midst of a large raid as they arrive). A boatload of supplies and almost a dozen townsfolk have been taken by these raiders, and it falls to the PCs to head out and rescue them. They'll have to navigate the perils of the swamp and find the Lizardfolk lair in some overgrown ruins, but there's a surprise waiting for them in the deepest chamber: A BIG ASS MONSTER WITH LAIR ACTIONS AND ALL THAT JAZZ!

As a relative newbie to DMing in 5e, my questions are: How big of a challenge can I realistically throw at this group? Especially if I'm not giving them a heads-up that there's something REALLY DANGEROUS as the Boss of the Lizardfolk

I'd love to go for something really iconic, like say, a CR7 Young Black Dragon (which could have some fun RP between the Black Dragonborn and the Lizardfolk who worship this monster). But is that too much for a group of 6 at lvl4-ish? Not enough? They've proven adept at focusing down single foes (especially with two rogues and the Druid learning to use her crowd of summons more effectively), so if a CR7 is appropriate for the group size & lvl, maybe I should be sure to include a few mooks in the fight too?

Any advice from DMs who have run encounters like this at this level range would be greatly appreciated

[PhoenixPhyre]

Core part of 5e encounter balance: action economy is key and overrides almost all else. 6 PCs is also quite a few.

6 players vs one monster will always result either in a cake-walk or a TPK (or at least a near-TPK). Even with lair and legendary actions. If you don't turn up the CR hard enough, the sheer difference in number of attacks will overwhelm it in short order. If you do...you're likely to one-shot PCs and then things go south quick. This is especially true since you're lacking in combat healing--once someone hits 0 they're likely to stay down since no one can cast healing word and the druid can't be everywhere.

Also, the lowest level legendary creature is the Unicorn at CR 5, then comes the CR 10 Aboleth.

I recommend instead using a much weaker enemy, but giving it a pseudo-lair action to summon help.

For example, initially they face the following:
A black dragon wyrmling (CR 2)
A lizardfolk King (CR 4)
and 3x lizardfolk (CR 1/2).

Every round (except the first) on initiative count 20, if the king is still alive he calls 1d3-1 more lizardfolk to the fight, down some stairs. If they block the stairs, they can stop the lizardfolk, but the lizardfolk can break down or bypass the blockage if someone's not there. Thus, the party has to split their attention between the big threats and the incoming hordes that, if not stopped, will overwhelm them.

The wyrmling will play keep-away with the party and try to use its breath as much as possible, not fearing to melt some lizardfolk. If the area has a high ceiling, he can fly up and avoid most of the damage (since you're short on good ranged damage). The king will try to keep a squad of lizardfolk between him and the party.

You can flavor this however you want. Also, make sure there's been at least two other encounters that day to drain some resources.

Edit: And how does the druid have summons at level 4? The first summoning spell is spell level 3 which doesn't start until character level 5.

[Unoriginal]

For example, initially they face the following:
A black dragon wyrmling (CR 2)
A lizardfolk King (CR 4)
and 3x lizardfolk (CR 1/2).


I'd say add more lizardfolks, or add a few kobolds.


If it's their one fight in the day, a party of 6 lvl 4 can dish a lot in a few rounds.

Or you could go for a Young Black Dragon and a few lizardfolks

[rahimka]

Chow does the druid have summons at level 4? The first summoning spell is spell level 3 which doesn't start until character level 5.

Lol, woops! Yeah, looks like the player and I both goofed (as I said, new to 5e), but it's only come up in 1 encounter so far.

Thanks for the excellent advice! The Wyrmling plus King/Queen and some mook lizardfolk (with the Lizard Chief and/or Wyrmling calling in a few more mooks each round) will be perfect. It fits actually fits nicely in the setting too: explaining why this dangerous creature is able to operate so close to the center of power in the kingdom. This little Wyrmling has recently arrived in the swamp and got the Lizards riled up, but the thing isn't so old or dangerous on its own that it should have been a bigger deal already.

(PLUS, it sets up nicely to borrow a page from the Giant himself and throw a vengeful dragon-momma at them later in the campaign)

[PhoenixPhyre]

A couple pieces of advice for new DMs--

* http://kobold.club is your friend. Mainly because it lets you search through all the published (and a lot of 3rd party) sources. No descriptions, but does have CR. It also handles the CR/XP math for you.

* Memorable fights are less about turning the difficulty to "meat grinder" than about making sure the players can't settle into a stock strategy of "surround it and beat it into the ground". Give something obvious in the environment for the players or the NPCs to do. For example, in this fight you might make it so there are two entrances. The thief rogue can (with Cunning Action and Fast Hands) cover both, leaving the rest of the party free(er) to lay the smack down. Or have things they can trigger, or keep the enemy from triggering. White room "and now we fight till one side dies" fights get boring fast.



I'd say add more lizardfolks, or add a few kobolds.


If it's their one fight in the day, a party of 6 lvl 4 can dish a lot in a few rounds.

Or you could go for a Young Black Dragon and a few lizardfolks

If it's the only fight of the day, I'd say add a couple more lizardfolk. But better to have a few fights (and a short rest or so) before hand. Let those hit die have meaning.

[Unoriginal]

Lol, woops! Yeah, looks like the player and I both goofed (as I said, new to 5e), but it's only come up in 1 encounter so far.

Thanks for the excellent advice! The Wyrmling plus King/Queen and some mook lizardfolk (with the Lizard Chief and/or Wyrmling calling in a few more mooks each round) will be perfect. It fits actually fits nicely in the setting too: explaining why this dangerous creature is able to operate so close to the center of power in the kingdom. This little Wyrmling has recently arrived in the swamp and got the Lizards riled up, but the thing isn't so old or dangerous on its own that it should have been a bigger deal already.

(PLUS, it sets up nicely to borrow a page from the Giant himself and throw a vengeful dragon-momma at them later in the campaign)

Remember that most creatures know when fleeing is for the best.

A wyrmling would flee rather than die, no matter their dragon pride.

[Callak_Remier]

Enviroment is key and often forgotten. Your not playing on a flat even grid. ( well you are but your not)