So, just ran the session with the Big T. It was AMAZING. I'm VERY glad I made this a Paragon Level encounter instead of epic-- with all the things my players could do at Paragon, I can hardly imagine how it could have held up against epic characters, even with much bigger numbers all around.
So, let me respond to the above criticisms...
1. Carapace: How the heck does that make sense? Firstly, its carapace is on its back. Secondly you seem to be nerfing melee classes here. I'm not against the whole 'climbing frame' thing - actually I like that. But surely its better if maybe attacks from a climbing character do more damage (or at the very least ignore its resist all 10).
Turns out, it doesn't nerf melee compared to ranged. Those that are dealing melee damage tend to have the athletics to make the checks needed. It worked really well, actually. The issue was that I wanted skill checks to be necessary in order to make melee attacks. Armoring its feet was the only way I could think to do that.
Ranged was far more nerfed. Its defenses against most ranged abilities (non-ac) are higher, it only takes half damage from ranged, and the ranged attackers quickly felt outmatched because when they did miss (more often than half the time) they ended up attacking a fellow party member instead due to the reflection. Melee didn't have to worry about that. In fact, my melee fighters only missed ONE check the whole fight!
2. Resilience: You know from the stunlock thread that I favour the idea that Solo monsters should be Immune to conditions until reduced to 25% hit points.
The main difference (apart from simplicity) being a Trait block with 1 line of text and not 14 - less for a DM to remember.
I still disagree, and I've talked about this with my players. They feel that being unable to have any effect at all with their special abilities until they've already almost won is no fun, and furthermore, once they got to that point, they have so many stunlocking abilities I might as well make the monster have 25% less HP anyway.
Speaking of which, I halved all HP for the external tarrasque to speed up the fight, due to advice I've found elsewhere. Made the fight drag out less, worked well. Basically meant that those outside killed the tarrasque only shortly after those inside killed the heart.
3. Bite: Ongoing damage 5 is too low, it should be minimum 10, more likely 15 though.
Due to being granted saving throws off turn, this never came up for the fighters outside the tarrasque. You may be right though.
4. Slam: I'm curious, how does the Tarrasque Slam a target?
By leaping up into the air, and body slamming into the target, and then burrowing through the ground dragging the poor sap in front of it as it goes.
It was cinematic and awesome. Definitely superhero stuff, as paragons should be.
The players got some good information on the tarrasque in advance of the fight, mostly by consulting gods and devils. They learned it needed to be killed outside and in, and the came prepared with acid resistance. The Rogue and Sorcerer headed inside, right off the bat trying to get into the mouth, readying actions and using acrobatics to do so. In fact, the rogue rode the tarrasque around for a while, getting smashed up by the burrowing in the process (using slam attacks for the roll and damage). The sorcerer readied an action to teleport into the mouth once it opened.
A battlemind and cleric stayed outside. There was much tunneling in the early part of the fight, while everyone was outside, a lot of slamming people into the stone and crushing them against rock. But once it was just the two, things were a little less interesting on the outside, aside from trying to kill civilians from time to time without getting mindspiked.
They initially mistakenly though that they only had to kill the heart, and those outside were just supposed to keep it occupied away from killing civilians, but when the regeneration popped up, they realized pretty quickly that they needed to keep the hurt up in order to put the thing down.
The gizzard tripped them up for a couple turns, as the sorcerer just dove down the throat first thing without looking at all, without even any light. The rogue helped him out. The sorcerer then landed in the acid, and felt confident for a while, having acid resist 20. But the ongoing acid kept mounting up.
In the meantime, the battlemind was practically having a one-on-one duel with the tarrasque, with minor support from a cleric keeping well back. He utilized an ability to force an attacker to reroll crits 50% of the time to GREAT effect, narrowly avoiding losing a limb from sharpness bite on a few occasions.
The sorcerer fought off the parasites while the rogue cut through the stomach. They swam through the fat while being chased by more parasites, which were fought off. They reached the heart chamber, and thought they had a straight shot to kill the thing... but got paralyzed quickly by the opportunity attacks they thought came out of nowhere.
The sorcerer actually fought the LUNGS, which I hadn't thought about, but I made it so that dealing 80 damage to a lung would cause the tarrasque to be dazed until it regenerated the lung damage. The rogue wrestled with being puched back and immobilized for a few turns, having poor will defense, but eventually got up there.
A lvl 16 rogue can kill the heart in two turns. One, using an action point. He did so.
After realizing that the tarrasque wasn't dead yet, the rogue stayed inside to keep the heart stabbed so it couldn't regen, while the sorcerer teleported out to join the battlemind. Together, they kept hammering out damage, but still never seemed to be doing enough, and as I mentioned, the sorcerer was getting frustrated by redirected attacks and frequently missing.
In the end, the tarrasque got a crit on the sorcerer, confirmed sharpness bite, and chomped off an arm. But since the battlemind had the tarrasque mindspiked, this ended up dealing nearly a hundred points of damage, bringing it to nearly dead-- practically a minion. The fight ended with the battlemind making a crit-athletics check to jump high into the air, Final-Fantasy Lancer Style, and thrusting his glaive through the Tarrasque's skull, nailing it to the ground.
It was exciting.