I was presented a concept for a one shot session from one of my players. He comes up with some strange ideas, and I'd like to see if this one would be viable:
The scenario goes that the Tarrasque has a prophesied date of awakening, so an elite order was created for the sole purpose of combating the creature to put it back in the ground. Using a combination of training courses over the course of many years (multiclassing into very specific classes), each of the group can become as large, if not larger than the Tarrasque and, for the lack of a better term, wrestle it to death.
My question is: Is there actually a combination of class features and spells that can push a character to get larger than a Tarrasque? And if it is, what kind of bonuses should such a character get upon reaching that size?