What does it take to kill a Tarrasque? We ran the numbers.

The Tarrasque is CR 30, and calibrating a fight against it is hard. So we ran the numbers in a simulator that plays every fight turn by turn under the 2024 rules: every attack, save, spell, reaction and legendary action. The parties were level 20, using the free-rules classes, with no magic items and no cheese tactics. Each party fought 120 times.

A few things that surprised us:

Four heroes never win. Not once in 120 fights, and every hero dies. Six heroes win 90% of the time. Seven win every fight.

Who you bring matters as much as how many. A Barbarian or a Monk as the sixth hero beats the standard party. Leave the Cleric at home and you win only half your fights.

Sword-swingers struggle. It resists weapon damage, magic weapons included, so the Fighter deals less than the Rogue. Irresistible Offense fixes that for the Fighter and barely matters for anyone else.

Casters have it worse than you'd think. It's immune to fire, its carapace stops attack-roll spells five times in six, and it saves with advantage. Our fire-built Sorcerer's Metamagic doesn't save it; Power Word Kill would.

Full write-up, with charts and a replay of one of the fights you can watch round by round:

https://longtabletools.com/blog/what-does-it-take-to-kill-a-tarrasque

If you've run the Tarrasque at your table, I'd like to hear how it compares. 

This is really cool! Thanks for sharing! I feel like I'm on the right track building a character that focuses on radiant and force damage