Test battle!!!

[SMac8988]

So my players are finishing designing and putting characters on to paper tonight and I was thinking something fun to do would be to let them have a big test battle to try all the features of their characters.

My idea would be to have it be a closed in cave system, maybe a few small tunnels running off that circle back around and connect into the large center chamber.

They are all level 7, and after rolling stats have rather strong stats across the board.

Team is:

7 Tempest Cleric Assimir, favoring casting and standing back.
7 Tranquil Monk Kenku, super big in talking fights out.
7 Wizard Dwarf, he got really high str and con as well as int and decided he will cast while battling with his axe.
7 favored Sorc, knowledge, half elf, mainly using fire spells as of now.
7 Moon Druid, Firblog, this is my least seasoned player and tends to make the most off the wall shifts and be overal entertaining.
And a golith luchador grapplers, 5 bear barb/2 rogue going thief set for fast hands and using manicals.

I was looking for advice on a challenging fight that would be more than just a hack and slash beat up. This would be an isolated fight with no link to the actual campaign, so anything is fair game. One large monster in the middle and a bunch of small in the tunnels would be ok too.

[EvilAnagram]

Night Hag coven with a catoblepas guard dog.

The hags will use their advanced casting to seriously damage the party and control the battlefield while the catoblepas keeps everyone poisoned and tanks the **** out of them.

It's a single encounter, so everyone should be blowing their wad from the get go, so it's okay to have a bit of a higher difficulty.

[SMac8988]

I plan to have it be a nearly deadly fight, so I'm ok with that. I haven't ran hags before, are they truly that deadly.

[EvilAnagram]

I plan to have it be a nearly deadly fight, so I'm ok with that. I haven't ran hags before, are they truly that deadly.
When they're in a coven their spellcasting increases and they become a higher CR. I'm AFB, but I think it's CR5 each, plus a CR5 catoblepas. Add in another catoblepas if you want to cement deadly status.

Edit: Nevermind, they're each CR 7 when in a coven.

[SMac8988]

I ended up putting them in a small ravine they fell into with a small top of a temple showing in a lake. As they approached they were attacked by crocodiles, when they just about killed the giant croc, I had a hydra spring from the water and attack. Also made the water ice cold, which did frost damage if they were standing waist deep or more.

They liked it, took a bit of time and knocked down 2 of them before it was over. So overal worked for my goal and was fun.