Galerius realized he needed to heal up and eat. 

"Bread, meat, and cheese, Willagee. Here's the money."

He gave the money to Willagee and slunk off into the corner to take a short rest.

"I know the Heroism spell since you mentioned it, but I really doubt it would help. But if you need the bravery to get close enough to cast Fly, you have it," Hatch said.

(What spells does Lia have? Do we have any other spellcasters?)

Throm sits at a table, leans forward and cradles his head in his hands. “It’s just not right” he mutters to himself. “We’re in a trap created by Mad Maggie, or whatever her true name is, possibly a goddess of chaos. There is a mythical creature of world crushing power not asleep on a mountaintop or under the earth but on a castle roof. It certainly wasn’t defeated in the highest room of the highest tower and forced into a stasis sleep. If the castle was built below it while it slept, the builders were more brave than anyone I have ever met. Waking it would be certain doom. No, this isn’t right.” Throm lifts his head and eyes and surveys the room. “Chaos, puzzles, trap. Chaos, puzzles, trap.” Throm slowly stands and modestly proffers, “What if none of this is real? What if all of it is some grand hoax, a group delusion? We know dispel magic won’t work on the barrier but what about on this table? If we are still in the original tavern and only meant to see an opulent piazza, could dispel magic give us a glimpse of what is real?”

Yawning and stretching after his nap, Galerius went up to the library. There he heard Throm mention the possibility of the tavern being a magical hoax. "Interesting," said the Dragonborn, rubbing his chin thoughtfully. "Does anyone know dispel magic?"

Quin said, "I don't haave Dispel Magic, but I have Major Image and Web. I think if we could lure the Tarrasque with Major Image to the edge of the balcony or whatever it is using Major image, maybe he would follow it right off the balcony and "fly" to the ground." 

"But that seems dangerous."  

"Polymorph would be perfect, but I don't have it. I don't get to trade out a spell except after a level up. A wizard, however, can change out a spell after a short rest."

Here are Quin's spells:

Cantrips:

• Create Bonfire
• Eldritch Blast
• Fire Bolt
• Light
• Mending
• Minor Illusion
• Prestidigitation
• Toll the Dead

1st Level:

• Chaos Bolt
• Find Familiar
• Hellish Rebuke
• Shield

2nd Level

• Branding Smite
• Mirror Image
• Misty Step
• Web

3rd Level

• Fly
• Hste
• Major Image
• Counterspell

"Well I think I have a plan. Fly works only on a willing creature, so we just need to make sure he's willing. We try Charm or something to get it in a good non-attacking mood, or we find a way to wake it without angering it. We create the illusion of something it wants, something it has to fly up to get to. Then you cast Fly. We just need to figure out what it would be willing to Fly to get to," Hatch suggested.

Bentley tells Quin his wand is a wand of binding.

What luck! The library also contains an extensive collection of spellbooks and spell scrolls, representing almost every spell known to exist ... except one. Unfortunately the Wish doesn't seem to be among the library's spells. 

Buck reports that Willagee appears to be mundane as far as magic goes, a simple commoner. Kardinya seems to have some limited magic, but has only seen her use simple cantrips to aid her in cooking and cleaning. Bentley seems quite capable in a variety of skills, but with no magic talent beyond the ability to use magic items. Many other patrons look to have magic ability, but whether they are willing to participate is doubtful.

Willagee isn't too knowledgeable about other planes. Others have tried escaping through planar travel and been unsuccessful. The tavern seems to be trapped in its own demiplane, without access to any other.
(In other words, any characters that previously joined would technically still be present, but if their players aren't actively posting, then their abilities will not be available for use.)

None of the books shed any light on how the tarrasque came to be at the top of the tower, neither does Willagee or Kardinya know. Bentley seems to think that the tarrasque was present before the castle though (otherwise the monster would have destroyed the building), suggesting that it was either built around it, or more likely that the tarrasque was magically transported to the tower top somehow. The tarrasque's sole objective is to eat the world. It awakens usually every few decades and rampages for a few days before falling asleep again. The fact is has apparently been present and asleep here for centuries is presumably an effect of the curse, just as the devils and dragons and everyone else's presence here bordered on the fringes of true reality.

Galerius knows that you can't believe everything you read. The most reliable information suggests that the tarrasque has significant resistance to magic, although whether that is the case when it is asleep is not stated. The bulk of information in the library is summarised here:

Monster Manual

Forgotten Realms wiki

Important things to note:
Saving Throws INT+5 WIS+9 CHA+9
Damage Immunities Fire, Poison; Bludgeoning, Piercing, and Slashing from Nonmagical Attacks
Condition Immunities Charmed, Frightened, Paralyzed, Poisoned

Legendary Resistance (3/Day). If the tarrasque fails a saving throw, it can choose to succeed instead.

Magic Resistance. The tarrasque has advantage on saving throws against spells and other magical effects.

"Also, according to the information, 'The tarrasque has advantage on saving throws against spells and other magical effects'".

(Lia's just a fighter with an interest in magic. She knows the cantrip Mage Hand due to her archetype, but I don't see that being incredibly helpful. Also I'm fairly sure there's an eldritch invocation for pact of the chain that allows you to deliver touch spells through your familiar. Is there any chance you have that Quin?)

(( Sorry, no Polymorph for Onyx... he's a warlock. But there's always True Polymorph. ))

"Wow! Quite the wealth of information on this creature is available. And thankfully, we have access to most of the spells we need, so long as someone can cast them."

Onyx frowned as he realized how difficult a task this would be. "You know... I'm going to go out on a limb and say this thing will awaken at the first spell cast on it. If it is so resistant to magic, it'll probably notice when it's targeted."

"I say we just decide what spells to try, but be ready to fight as soon as we do. He can't be charmed, but Fly, Polymorph and True Polymorph still seem to be our best bets. I'll grab a spell scroll for Fly, and just in case, one for True Polymorph. If he's unwilling to accept flight, we'll have to hit him with enough spells to wear him down so a polymorph can take effect. Hopefully we'll be able to last long enough for that to happen."

Quote from Vakanai >>

"Well I think I have a plan. Fly works only on a willing creature, so we just need to make sure he's willing. We try Charm or something to get it in a good non-attacking mood, or we find a way to wake it without angering it. We create the illusion of something it wants, something it has to fly up to get to. Then you cast Fly. We just need to figure out what it would be willing to Fly to get to," Hatch suggested.

 "That was my plan originally, by using Awaken. Awaken would have made the tarrasque a willing creature. We could hit him with it while he was asleep still and then hit him with the Fly spell. Then I read that he can't be charmed." Said Quin. 

Quin is terribly excited to learn that there are spell scrolls in the library with everything except the wish spell. 

She talks to the others. 

"We know that three times a day, the Tarrasque can just say that he doesn't get hit on a hit. In other words, say we cast something on him that would actually hit him for damage. He can choose not to take the hit three different times."  So we have to find a way around that. Either put ourselves in danger and keep firing magic at him until 3 of our spells hit him and he ignores the hit and then do the real spells we want to do, and then by then we might all be bloody and wounded and so on. 

He can't be harmed by Fire, Poison; Bludgeoning, Piercing, and Slashing from Nonmagical Attacks. He is immune to any non magical attack then, that is thrown at him as I see it. 

He is immune to Charmed, Frightened, Paralyzed, Poisoned. 

He is resistant to magic but not impervious to it. 

The tarrasque has advantage on saving throws against spells and other magical effects. So that means that if there is a saving throw he would have to make to avoid the magic effect dealt to him, he gets to roll to save twice. But if the magic effect that we use is instantaneous, and doesn't require a saving throw, like Magic Missile, then the magic affects him. Of course you can't use Magic Missile or Lightning Bolt or any other line magic because it would be reflected right back at us off of his shiny bug shell like body.

There's no way to reason with the thing because it's intelligence is so low that he's barely sentient. 

The reason we need the spell "Heroism" is in case the Tarrasque wakes up before we  have finished our plan. If whoever is casting spells suddenly becomes frightened, we all lose. 

There are other ways to give extra power to magic casters as well.  

True Polymorph gives him the ability to make two Wisdom saving throws. He has a +9 to his Wisdom Saves and he has Advantage on any save he makes so let's look at other things we could do first.  Let's look at *everything* we can do to find the best way to avoid becoming a meal for him. All he wants to do is eat. That is what motivates him. 

First, we cast  Invunerability on the spellcasters involved.

Second, we use "Summon Giant Insect" to get the Tarrasque to use up his 3 daily saves. 

There's a spell called "Reverse Gravity" that is often overlooked but it has potential. If he is hit with that he doesn't really have as good a chance as he would against True Polymorph. He can only try to grab on to something that would actually keep him from flying upward (as if falling because gravity is reversed). There's probably nothing he can grab on to successfully even if he were able to successfully make a Dexterity saving throw. Luckily he has a +0 modifier to Dexterity anyway. I actually think that Reverse Gravity has a chance to work. He would fall or fly to the ceiling. The spell lasts for one minute. If he hits the ceiling at his weight of 130 tons, he will probably keep flying up right through the ceiling while we all run like hell. At that point, we will know if we have successfully made five fly because either we will be able to leave or we won't.  If we are unable to leave, the Tarrasque will fall back down once the spell ends. And in that case, this castle will probably end too.

If we have failed, we can cast "Guards and Wards" on the castle but I'm not sure it would save us from a falling 130 ton creature.

So. Does anybody have a better idea?  Before we make our final decision, read through the Reverse Gravity spell. And remember, even though True Polymorph would be awesome, it's very likely he would save against our attempts to cast it because it's a wisdom save and he has a +9 on wisdom saves. All he would need to roll is an 8 or 9 or so to beat it and he would get to roll twice.

Quote from RodTheBard >>

(( Sorry, no Polymorph for Onyx... he's a warlock. But there's always True Polymorph. ))

"Wow! Quite the wealth of information on this creature is available. And thankfully, we have access to most of the spells we need, so long as someone can cast them."

Onyx frowned as he realized how difficult a task this would be. "You know... I'm going to go out on a limb and say this thing will awaken at the first spell cast on it. If it is so resistant to magic, it'll probably notice when it's targeted."

"I say we just decide what spells to try, but be ready to fight as soon as we do. He can't be charmed, but Fly, Polymorph and True Polymorph still seem to be our best bets. I'll grab a spell scroll for Fly, and just in case, one for True Polymorph. If he's unwilling to accept flight, we'll have to hit him with enough spells to wear him down so a polymorph can take effect. Hopefully we'll be able to last long enough for that to happen."

 If we have to fight this thing with our magics and we have say 60 Hit Points, remember he has nearly 700. To wear him down with us remaining alive would be impossible. You're right about him noticing if we attack. That's why I suggest the Summon Giant Insect spell. Get him to use up his 3 daily saves, target him with Reverse Gravity that he can't in reality save against and he flies. Right through the roof. We just have to make sure that we spellcasters who are casting the spells have Invulnerability first because we are likely to go flying right through the roof with him. Unless the instant he flies, the curse is over.

"Does he need to be alive? If not, we could just kill him and then make him fly. And when I say kill, I mean kill. Not fight, not battle, but kill," Hatch suggested, looking at all the spells now available and forming a serious and disgusted frown.

"I was told that if you need something dead you should just skip fighting it and kill it. In a case like this where fire and poison isn't an option, you simply need to suffocate it. All living things need to breathe. It has advantage against magic, but the room it sleeps in doesn't. We seal every crack, cut the top floor off from the rest of the building. And we set up some magic fires that never touch the monster and won't burn the room down, but will consume all of the oxygen. The tarrasque dies never once being targeted or attacked, ideally sleeping through the whole plan. It worked on some dwarves my sadistic caretaker felt were mining too close to her cave, it could work here..."

Quote from Crabitha >>

 If we have to fight this thing with our magics and we have say 60 Hit Points, remember he has nearly 700. To wear him down with us remaining alive would be impossible. You're right about him noticing if we attack. That's why I suggest the Summon Giant Insect spell. Get him to use up his 3 daily saves, target him with Reverse Gravity that he can't in reality save against and he flies. Right through the roof. We just have to make sure that we spellcasters who are casting the spells have Invulnerability first because we are likely to go flying right through the roof with him. Unless the instant he flies, the curse is over.

Onyx nodded. He was impressed; it sounded reasonable. Use summoned beings to do most of the heavy lifting, while the rest of them waited for their opening.

"I like that idea," he said. "One good thing at least; he pretty much is already on the roof, so if he does get flung into the air, there's nothing for him to crash into."

He turned towars Hatch and shrugged.

"Sorry, sir... sealing it up might actually work, but from what I saw, the fifth "floor" is just open to the air."

(( Onyx will look for scrolls of Summon Lesser Demons, Summon Greater Demon and Conjure Fey, along with the previous three he mentioned. ))

"I don't know if a dead creature can be "willing" to fly.  I actually think it would be easier to kill the thing than to make it fly. But the point is we need to make it fly for us to get out of here.

I'm feeling like my plan would work. First, give us spellcasters invulnerability, then make him use up his 3 free saves with the giant insects attacking him. They do what we tell them.  Then cast Reverse Gravity. I've seen it used before and it's very effective. It's not like levitate where someone floats up, this is gravity. That thing weighs 130 tons. He's going to fly."

"Well, at least we have an idea, although it is oddly disappointing. There's really nothing at all most of us to do but stay out of the way and hope for the success of the magic casters. Weird, to be disappointed because I am unneeded, but the important part is that we will be able to finally leave this place," Hatch said. He had felt so involved and a part of this, but the truth was the outcome could only be decided by the far more magically capable.

"You have the plan, the scrolls are all here, so there's no need to wait around any further. Everyone is counting on you spell casters. Gods speed," he said, before heading off to find Bentley.

"This place have a gym or something? Training area? I need to hit my axes in something," he asked.

"Oh no. I didn't mean to make anybody feel left out, Hatch. I had thought we would all be together to enact the plan. Besides, I am thinking that if things go wrong, our only chance will be to fight him and we will need everyone for that. Especially our fighters. If you don't have a magical weapon, it's very easy to make your weapon magic. That's a very easy spell to cast on weapons. Adding a +1 to whatever weapon you are using makes it magic. So he won't be immune to slashing, piercing or bludgeoning. The reason I suggested using giant insects to attack him is so that he would attack them instead of us.

But we need you there for not just back up but for support. You've done so much to get us this far. I couldn't solve a single riddle. You and Lia solved them all. We need you to be with us on this. You've essentially been the leader throughout most of this crazy curse. If you're not with us I'm going to feel leaderless. And if this doesn't work, we have a better chance of killing the thing with you there. I will make your axes magic and add +1 to them. I think the riddle for this last curse was meant for us to find a way to use magic in a way that gives us the best chance to succeed. I haven't contributed to a single riddle until now and I was only able to because I have experience as a spellcaster and like you understand the strategy of position and other things I don't in battle, this is the one thing I know how to strategize because I understand how the creature we face is going to be the most likely to succeed or fail against what kind of magic. It's the first time I've felt like I was useful really. I need your support."

"How do I make my weapon magic?"