Lucky dex save: 3

Joy realizes her mistake just a moment too late, bracing herself to get hit by the cut grass.

The stocks of grass snag and respond by wrapping themselves around whatever parts of her body that they attach themselves to. A lancing, burning sensation radiates from various contact points, even working their way through articulation points in her armor. They stick to her like velcro, as the barbs work their way into her flesh. 

DM: Joy takes 3 Necrotic Damage, but suffers no additional ill effect, as the ghostgrass is not rooted to anything that would allow it to Restrain her. Magical healing will force the barbs out immediately. 

The paladin lets out a cry of pain and annoyance as the grass clings to her, dropping her sword and focusing the best she can to heal herself and force out as many barbs as possible.

Lay on Hands, +2 HP

"Ugh, t-there. We need to get moving or they'll leave us in the dust...er, sediment."

Joy gives a sigh of slight relief as she picks her sword back up and sheaths it. She notices the cut grass still lingering, shifting slightly in the tide. Not wanting anyone else in her party to stumble into it...and getting an idea, she tries to collect some in her pouches, not particularly dissuaded by the pain.

Dex save 1: 7

Dex save 2: 17

As Joy reaches out her hand to grab the stocks of seagrass, they nip her again, searing her nerves with neurotoxin. 

DM: Joy takes 2 points of Necromantic Damage and (RP only) feels like her hands are on fire until she receives another magical healing. 

She fights through the pain and stuffs three stocks of the pain-inducing ghostgrass into a pouch and makes it to the other side of the cavern in the process. 

DM: Everyone else will need a Dexterity Saving Throw, DC 12, to follow Riven carefully around the ghostgrass. 

DM: Berk succeeds with a natural 20, for a 22 total. 

Ylis keeps a little bit of distance at says, "Prancing ponies, toasty toesies." and casts [spells]Create Bonfire[spells] on the patch of ghostweed. DC 13 Dex save vs  8 Fire damage

She's not sure if it'll work but it's worth a try.

Randa keeps pace with Riven trying to use her light to lead the others through safely...

Dex Save- 10

As the Fellowship follow Riven along the rope, Ylis starts a magical fire on the ghostgrass. It fails to ignite, but it does burn. After a few moments, the impossible underwater blaze burns away the ghostgrass and the party is able to move freely. 

Fortunately, the less dexterous members of the party were saved by the spell before they suffered any ill effects.