Determining that the green mass is the bigger threat, despite the crustacean still in her face, a weakened Elyona casts moonbeam on the doorway area the green mass is spilling out of.

5 Radiant damage on the start of it's turn; other affects for shape changers, but I presume that's not in effect here.

Note to self and DM: this is a concentration spell.  

OOC: additional notes to self: divine smite and moonbeam spell slots marked off.

Toots stabs at the crustacean with Rave- (Attack: 30 Damage: 18), and then whirls her spiritual weapon at the slime- (Attack: 17 Damage: 19).

CON save 15

The green mass bubbles and pops under the burning moonlight and holy hammer. The skeleton is badly damaged by Tommary and is finished off by the spider!

Finally, Toots thrusts her trident completely through the crustacean, shattering its shell making fall to the floor in two slimy chunks.

Ilyara

OOC: Sorry all, day was a little fraught yesterday.  Everything's fine, just didn't have a lot of focus to spare q_q

Lessee.

IC: With relatively little ability to do anything about the mass of Evil Fungus, Ilyara mutters a curse under her breath and looks around at her wounded party.  "Anybody got that?" she asks quickly, before invoking a brief chant and allowing healing energies to wash over the entire crew including their spider guide.  It wasn't much healing energy, but it would help offset the accumulated harm from the acid floor and general combat.

"If nobody can stop the acid, we need to leave!"

{MHW HP roll: 4.  Watch it be four whole points, dumb fox.  Heh.}

Heal recorded. OOC: Thanks, Toots needed that.

OOC: Heal recorded.  Thanks, Elyona needed it too.  

"Tommary's firebomb seemed clear part of the acid: can someone try burning it?"

Unwilling to use her crossbow on the entity lest more acid be spewed, Elyona backs up a bit from edge of the acid and continues to concentrate on the moonbeam on the green cute.  She holds her flaming sword at the ready in case more creatures appear.

Elyona will hold her attack, and attack only if another creature emergences from the green cube and gets within melee range of her.  

Moonbeam damage on the cube's next turn:  8 CON 16 save for 1/2 damage.  Moonbeam round 2/10 (realized I should be tracking time for the duration)

OOC: would you like me to roll for a potential attack related to E's held action, or wait until we know if it is necessary?  In my Saturday game, we had a discussion about whether or not characters with multi-attack can attack more than once when holding their action.  After checking Crawford's answer to that question, I ruled no.  (Actually, one of my players was the first to suggest that was the case...it become a question with another player held their character's action).  I will presume that is the rule here unless you tell us otherwise. 

OOC: So I know for next turn: are there still oil flames anywhere in the room Ilyara could spread to the acid?  And we'll all just ignore how burning caustic acidic chemicals usually creates extremely toxic smoke/vapor because nobody needs that much science in their D&D.

I'll make a case for Control Flames yet!

EDIT: I feel like having to burn your reaction to trigger the held action should be enough of a penalty for held attacks.  RAW or not, you should still get the full effect of your action even if you have to hold it for off-turn use.  It helps players who want to exercise some greater tactical work in their play and enables them to adapt to the situation on the battlefield better.  Besides, Extra Attack doesn't say you have to take The Attack Action on your turn to get the benefits of Extra Attacks, does it?

OOC: It is a held Action and Extra Attack just says when you do your action. The Ready action lets you cast full action spells so you can get your multiple swings.

The fuel for the fire was the body of the crustacean so it has burned out.

Ilyara only used Bonus Action so far.

OOC: Oh that's right MHW is a bonus action.  Derp.  I completely forgot.  Well all right then.

IC:
As she calls out for help, Ilyara reaches down to her TactiPockets and pulls free one of her flasks of oil.  "Somebody got a light?!" she yells as she chucks the flask into the hex right above 1209 whose number is too obscured by table for me to see, letting it shatter and spread oil for the burning.

Toots tries to prestidigitate the acid away in the space directly in front of Elyona with her action, and with her bonus action she swings away again at the slime with her glowing mallet of doom- (Attack: 28 Damage: 10).

Ilyara tosses a flask of oil which shatters on the floor.

Two skeletons push their way through the clear membrane wall with a little splash of fluid.

A tentacle also erupts from the green mass trying to strike Toots!

Whap! Attack: 26 Damage: 12 Acid Damage

CON save for Moonbeam 25

Elyona needs to move in order to attack the skeleton.

Toots' hammer slaps the mass making it jiggle wobble.

Prestidigitation does nothing to the acid slime.

Tommary, Elyona, Ilyara go!

Quote from Wysperra >>

A tentacle also erupts from the green mass trying to strike Toots!

Whap! Attack: 19 Damage: 14 Acid Damage

Damage recorded

Quote from Wysperra >>

Toots' hammer slaps the mass making it jiggle wobble.

Prestidigitation does nothing to the acid slime.

Slap? Jiggle wobble? The 28 hit though, right?

Sorry gang, Toots tried to clear up some of the acid, but to no avail. 🤷‍♂️

Tommary casts 3rd level shatter at the blob and skeletons to shake things up before Elyona gets in there.  20 Thunder damage, or 15 CON save for half damage.

"I need a light before I can burn this crap away!" Ilyara yelled, striking Rilia's pommel again to ring some bells targeting the gelatinous mass.  Noting things are looking worse rather than better, she also invokews another brief chant, breezing more healing energies to the crew.

{Toll the Dead, Wis 15 save against 13 necrotic damage.
MHW: 7 healing to everyone including spider.  I am almost out of those guys, Ilyara is not a healy cleric.}

Question:  Is the oil on the acid close enough to Elyona for her to try to light it on fire with her flametongue sword?  Does she have reason to believe that would work?

If the answer to both of those questions are yes, that's what she will do this turn.

If not, and if she can reach the skeletons without getting in the acid, she will do so and will attack them (presuming that they are still standing). Attack rolls if that's the case:

Attack: 23 Damage: 22

Attack: 14 Damage: 18

Moonbeam damage at top of Green cube's turn: 17 radiant damage 1/2 damage on a CON 16 save

Is the oil close enough to Toots for her to ignite it with prestidigitation?