The attack roll that killed Cinder was...apparently not well-explained.
In D&D 3.5, natural twenties always hit what you are attacking, and you roll again to see if you critically hit the enemy. This roll is basically another attack roll; if it beats the enemy's Armor Class, you roll damage twice and add them together. (There are some exceptions; axes and some other weapons roll triple, quadruple, or in a few cases quintuple damage, and some sources of damage aren't multiplied, but that's not important right now.)
I'm not sure how natural twenties interact with situations where you might hit something other than what you're aiming at; my gaming groups always take the relatively small penalty and avoid hitting their friends. It could mean you automatically hit your intended target, or that you automatically hit a random target. The latter seemed more dramatically appropriate.
And now for the big question: How did the attack critically hit Cinder, but it wouldn't have critically hit the monster? To understand this, we need to look at Armor Classes. The monster had an Armor Class of sixteen, and Cinder's is eleven...with Dexterity bonuses. But they were grappling, which means you lose your Dexterity bonus to Armor Class, reducing the monster's Armor Class to twelve and Cinder's to only ten—low enough for the critical hit to be confirmed.
There are a couple of arguments against this. You could argue a natural twenty means you hit your target, regardless of chances to do something else. You could argue that the wording of the monster's ability means the target doesn't count as grappling. Perhaps the characters would argue that, to save Cinder's character. But it's too late now.
"She's not coming back?" Roman said.
"Not for this adventure," Emerald replied. "I'll leave a couple doors open, but…"
"Not today?" Mercury said.
"Not today."
Mercury sighed. "Typical."
"We'll just have to go on without a cursed wizard," Roman said.
Emerald closed her eyes. "It's not just that, it's—"
"I know," Roman said. "And you might have worked for Cinder longer, but I know her pretty well—and I've known her type longer than you've been breathing. Leave Cinder alone to brood for a while, that's the best. Work on patching things up when she's ready to come back and start ordering you around."
"What do you mean, you know her type?" Adam asked.
"You're probably older than the kids, Horny, but I'm still pretty sure I worked for my first megalomaniac wannabe-scourge before those big mean humies killed your favorite aunt or whatever," Roman said. "They're all the same. Try to hit the kingdom where it hurts and get their attention, get their deeds in big print on the front page, escalate. Eventually they all either run out of capital or go out with a boom. Taking over Atlas's latest potential superweapon or unleashing a plague on a kingdom or bombing the comms tower, something big and showy like that turns bad when they don't realize that things like that are pretty damn hard."
"Cinder isn't just another megalomaniacal scourge," Emerald said.
"Scourge wanna-be," Mercury said. "And she kinda is."
Emerald sighed. "What's your point, Roman?"
"Trust me when I talk about Cinder," Roman said. "She's good at the strategic side, but she tends towards tactical gaffes—"
"Tell me about it," Mercury said.
"—overestimating assets she could gain from various ventures, and if I'm not mistaken, her top-level planning is nonexistent." Roman sighed. "Sooner or later, those flaws will lead to her downfall and anyone who doesn't abandon ship when they have the chance is going down with it."
"Cheerful," Adam said.
"I don't think you can bail out of this one," Emerald said. "You're the face of this operation."
"Not the first time," Roman said. "But I'm ready to delve back into the dice and dungeons. Who's with me?"
Neo raised her hand, followed by Mercury. Adam shrugged and raised his hand. After a moment, Emerald sighed and raised her hand.
"Great," Roman said. "So, we're at the dungeon?"
"You are," Emerald said. "At least, you're now in the right area. It'll take a bit to find the exact place—"
"Or we could wait, see when the kidnappers find us, and ambush whoever they send to deal with us," Mercury said. "Kinda like our plan at the town, except they'd be a bit more expecting us and we'd be a lot more together."
"One of those is better than the other," Roman said. "What other options do we have?"
"Search the woods, hope we don't get ambushed, and hope they didn't lay an ambush at the entrance to their lair," Adam said. "I prefer Mercury's plan."
"...Well," Roman said, "when you put it like that, I can't really argue. Any ideas for attracting their attention?"
"Fire?" Neo said.
"Oh, good, we've still got a part-time pyromaniac," Mercury said.
Neo smiled and nodded.
"I'm not sure how that would attract attention towards us, specifically," Roman said. "I'm not even sure it would attract the kidnappers' attention at all, unless they were druids or their own home started burning. Which wouldn't be good."
"Why?" Neo said.
"The captives would burn, too," Adam said.
"Oh. 'Sbad."
"A little, yeah," Mercury said. "Especially since we'd be torching not only the victims-slash-quest-rewards, but also any chance of figuring out what's going on and basically a level's worth of treasure and XP."
"No fire," Neo said.
"No fire," Roman repeated. "Other ideas?"
"We need something that would get their attention, without making it obvious that we're trying to," Mercury said. "And it needs to leave our stuff guarded, and more importantly, we need to not split the party."
"We've got that squire guy, don't we?" Roman said. "We could send him in as a distraction."
"No," Adam said. "Sir Lane probably wants us to return him in one piece. Besides, if the enemy ambushes our squire, we'll never see them, let alone be able to capture one."
"Wait—Sir Lane?" Mercury coughed. "Like, steak?"
Emerald sighed. "I've said his name about a dozen times, and now you see that?"
"Yeah, but—seriously?"
"Gimme a break, it's better than King Crabbe."
Adam said, "It's a little silly, but—"
"King Crabbe was an elf," Emerald said. "Who had a gargoyle chancellor, but that's another story."
Mercury sighed. "Will I ever live that campaign down?"
"You don't have any other campaigns to live down, so..." Emerald shook her head.
"I like mocking Mercury as much as the next person," Roman said, "and more if Neo or Adam Killjoy—"
"Taurus," Adam growled.
"—is next, but let's get back to ideas. Distractions…"
"Maybe we could just wander around," Mercury said. "I mean, they'll surely have scouts?"
"They might," Roman said, "but they might figure that the best way to avoid being noticed is to avoid sending people out when they don't need to."
"They might not have the manpower," Adam said. "Armies scout, but the kidnappers presumably don't have an army of people, otherwise they'd be invading and raiding rather than covertly kidnapping people."
"This from the faunus supremacist," Roman said. "Remind me never to let him have an army."
Adam glared at Roman for approximately ten seconds before continuing. "They likely have hunters or something similar, to get food, but we wouldn't know them from village or tribal hunters without them attacking us."
"Which they wouldn't, because they aren't idiots," Mercury said. "Unless they are idiots, but that would make our job too easy, now wouldn't it?"
"Yup," Emerald said.
"We have a druid," Adam said. "How long can you summon animals for?"
"One round," Mercury and Roman said at roughly the same time.
"That's six seconds?" Adam asked.
Everyone at the table except Neo nodded.
"Not long enough to be useful."
"Outside of combat," Mercury said. "And in combat, really, since all I can summon are things like monkeys and octopi."
Neo looked up with a smile and attempted puppy-dog eyes.
"It's a little octopus," Mercury said. "Small. Like, halfling-sized or dog-sized."
Neo's eyes widened at the mention of dogs.
"It would only last for six seconds," Roman said.
Neo's smile faded.
"Dude, there's something wrong with Neo," Mercury said.
Neo, naturally, responded by kicking Mercury under the table.
"I think she just wants a pet octopus," Roman said.
Neo nodded without taking much attention off of kicking Mercury.
"Better," Mercury said, "but still kinda weird." He began kicking back.
Adam had begun flipping through the Player's Handbook when Neo began silently begging Mercury for an octopus. "If we waited for Artemis to prepare more spells...never mind, none of these would help. Guidance is an overrated spell, you know?"
"It's a cantrip," Mercury said. "What do you expect?"
"Technically, divine ones are orisons," Roman said.
"Everyone calls 'em cantrips anyways," Mercury said. "Rolls off the tongue better. Pretty sure there was a classic spell called cantrip, too."
"Irrelevant," Adam said. "'Guidance' makes it sound...useful, impressive. Like you're getting divine inspiration on your quest. A plus one bonus to one roll? You get more guidance from a gnome with a lute strumming cheerily."
"Don't dis gnomes, Loom," Mercury said. "They're the spooniest race."
Roman raised his visible eyebrow. "'Spooniest'?"
"It means—"
Neo suddenly stopped kicking Mercury. "Pyre!" she said.
Mercury sighed. "No, Neo, it doesn't mean that."
"No, distraction!"
"We already said no fire," Roman said.
"Not everything," Neo said, "just Cinder."
"Like...a funeral?" Adam said.
Mercury nodded. "It's something like...raise dead is fourth level?"
"Fifth," Roman said.
"Then it's something like five hundred gold pieces for raise dead, not counting diamonds. We don't have anywhere near the cash. Reincarnate doesn't need more than ashes, and it's probably not more expensive."
Adam looked up from the book. "Raise dead requires five thousand gold pieces of diamonds. Reincarnate...is lower-level and only costs one thousand, in oils. It's also a lower-level spell, although a druid one."
"Why does…" It dawned on Mercury. "Ah. If it's a problem, you can just leave me behind. We only need ashes for reincarnate, and I'm pretty sure it works for longer after death."
"Cinder's going to be pissed if she doesn't come back human," Emerald said.
"If she comes back at all," Mercury said. "Which she wouldn't if we had to abandon her corpse. Ashes are easier to carry."
"So we're burning Delilah's body?" Adam said.
"And what a hell of a pyre it'll be," Roman said. "Sure to attract attention."
"Great," Mercury said. "Who has an axe?"
No one answered.
"I'll let you retroactively spend a few gold on some woodsman's axes," Emerald said. "This is a good plan, twenty experience to Neo, I'm not letting it die that easily."
"One for each of us?" Roman asked.
"Sure," Mercury said.
"Why wouldn't we have gotten five?" Adam asked.
"Do you really think Delilah would have deigned to chop wood?" Roman asked.
"...Touche. Four it is."
"So, we just cut down some trees, toss Delilah's body on them after stripping her of anything we could sell or use, and set it on fire?" Mercury asked.
"Does that include clothes?" Roman asked.
"Sure," Mercury said. "It'll help pay the seventy gold, two silver she owes the party."
Neo winced in disgust.
Adam frowned. "I'll ignore that. But we should say some eulogies."
"Sure," Mercury said.
"In-character."
"Oh."
Emerald glanced at the door to the room. "I'd give out roleplaying XP for good ones."
"Most of our characters barely knew her," Roman said.
"Do your best," Emerald said.
"I'll start," Mercury said. "Let's see...'I haven't known Delilah for all that long. When I met her, she tempted me out of the druidic garden I grew up in. She was a bit harsh, got us in trouble more often than I can count, and was a bit prone to setting fires, but she took care of me like a friend. I guess she was one. An unlucky friend who managed to fumble more often than not, a bit prone to embarrassing everyone, but no one's perfect; her heart was in the right place, and even if the bad stuff's more memorable, I'm probably better off with her than without.
"'I feel like Delilah, me, and you guys would have made a damn good team if Neo hadn't accidentally decapitated her. We could have done great things, you know. We'd know adventures, things Delilah will never see. We could go out of the kingdom and back...go to the frontiers, you know. We could have been standing on the deck of a ship bound for Punitive Camps with sweat in our eyes watching ships fight off the coast of...whatever continent this is. Feel the wind in our hair, riding test boats off the black waters and see an attack fleet burn like a match and disappear.'" Mercury sighed. "'But these—"
Cinder entered the room.
"You're back?" Emerald said.
"I've changed my mind," Cinder said. "Out of curiosity...are you holding a funeral for my character?"
"Yes," Emerald said quickly.
"That's...kind. I...appreciate it." Cinder looked around the table. "I...may have been a bit harsh. I know Neo didn't mean to kill my character, that the rest of you certainly didn't."
"That's low-level D&D," Emerald said. "One bad roll and you're toast. Makes the high levels, when you're basically demigods, all the more satisfying."
Cinder smiled. "I look forward to it."
"Demigods isn't entirely accurate for casters," Mercury said.
"Oh?"
"No, high-level spellcasters are more like...well...gods."
Cinder smiled even more.
I didn't actually have that conclusion in mind when I started writing the chapter. I don't really plan things much on the chapter level...and being able to organically create moments like this is why.
Quick note: As I mentioned twenty chapters ago, I'm doing this for the RWBY subreddit's monthly fanfic and art challenge. If you like Crypts and Criminals, I'd appreciate you going there and voting for it.
I promise this is the last you'll hear of that.