RPG geekery to follow.
For those unfamiliar: in D&D, the Tarrasque is a massive,
The danger here lies in unleashing a Tarrasque on an unsuspecting party. That’s just uninteresting.
Were I to use a Tarrasque in a game, I think it’d be a known threat. Let’s say, an evil sorcerer threatens to unleash a Tarrasque, or there’s a legend that the Tarrasque will be released if certain conditions are met.
So, the story can build up to the release of the Tarrasque.
The danger here lies in the implied assumption that the players can stop the Tarrasque’s release. To counter that, I’d add a twist:
A sorcerer has discovered that, under certain conditions, he can summon a Tarrasque that is under his control. Once the players encounter the sorcerer, he’s in the middle of the ritual. The sorcerer turns on the party. The party kills the sorcerer, or otherwise breaks his concentration and affects the ritual. While the Tarrasque does appear, it is no longer under the sorcerer’s control.
One other interesting idea: if the Tarrasque does rampage across the world, damage wide swaths of it, one could build a small campaign setting around a D&D world that’s picking up the pieces from a Tarrasque attack. There’d be tremendous amounts of work to be done, securing supply lines and rebuilding, as evil races take this opportunity to loot defenseless towns.
Much could be done.