When the Third Edition Monster Manual came out in 2000, its version of the tarrasque was bigger and badder than ever. The stat block included an Advancement line, which left open-ended just how much more powerful the DM could make it. That one little line of text inspired me with the first kernel of a new campaign setting. In all editions, the tarrasque is described as lying dormant for long periods of time, then reappears to ravage the countryside until it either sates its monstrous appetite, or is destroyed or driven off by a party of very high level adventurers. I thought what if, when the tarrasque fights (and frequently defeats) these heroes, it gains experience as well? Each time it reappears, it's marginally more powerful (perhaps adding a new Hit Die every few appearances?), which makes it an increasingly bigger challenge for future adventurers. Heroes who thought themselves prepared for the fight could be in for a nasty surprise when they discover too late that their carefully researched creature lore was woefully out of date.
For this new campaign, I decided to dramatically increase the time between the tarrasque's appearances, with intervals averaging around 30 years--roughly a human generation--instead of a few dozen months. This would enhance the creature's mystique, and give me a longer cycle to work into the world's history. After all, such a primal source of destruction could easily shift the balance of power in any region in which it appears, and even topple civiliizations. The player characters in this campaign would be the heroes destined to face the tarrasque in their generation, when the "Time of the Tarrasque" came again. This will be the most ambitious campaign I've ever run, and the first I've run from 1st level to 20th (or higher). Fortunately, the core of my regular gaming group have been playing together for over 10 years, and even survived a cross-country move intact, so I feel pretty confident that we'll still be playing together for the time we'll need to complete such a long-term game.
My notes for the campaign were originally written for D&D v.3.5, and I was still puttering with it when Fourth Edition was released. That system's tarrasque was recast as an abomination that could never be truly destroyed, only banished back to the world's core when "killed." That idea intrigued me, but I eventually decided that I did not like the Fourth Edition rules well enough to run a long campaign using them. I eventually settled on the Pathfinder RPG for "Time of the Tarrasque." In that system, the beast's stats were derived from the v.3.5 Monster Manual, but built upon the idea that it could not be killed, only driven off or banished for a time. And most importantly, Pathfinder is fully compatible with v.3.5, so while my copious notes would need to be updated, I wouldn't have to start over from scratch.
Over the past year, I have been gearing up to finally start running the campaign. I created a wiki to provide background information to my players, and we started discussing campaign starting points and character ideas. They have built their 1st-level characters, but are still fleshing out backgrounds. We'll start the new campaign once I've finished running my last big adventure for Freeport. I'll be blogging more about the "Time of the Tarrasque" setting as that time approaches, and continuing as the campaign progresses. My recent cactus leshy post was written for the desert frontier region where the main campaign will begin. Expect more information about this "Lands of the Sun" sub-setting soon!