Tarrasques rock very hard indeed, but they're an extreme end-game ploy. By the time you can manage to get a decent team of Tarrasques into the field, the game is probably over....
That said, I had a blast with Team Tarrasque in a SP game a while ago. One GoR'ed Tarrasque who had been empowered to S4 was leading a strike force of
more Tarrasques all over the map with judicious use of Gateway. Utterly inefficient, but very fun.
