I don't know whether anyone has already posted this link but here's a nice article titled "Seven Ways to Kill the Tarrasque on thirteen experience levels or less". http://www.cs.cmu.edu/~dkb1/dnd/tarrasque.txt
The most powerful createable character in D&D universe is Pun-pun the kobold. A level3 mage or so.(exact levels vary). Google, you will not be disappointed. This kobold owns all.
Those tactics are good @premidion_start, but if Tarrasque was to be added on BG II, none of them would be applicable because of engine limitations. Besides if tarrasque eventually comes to BG II, it will be in ToB, with a party lvl 20+, 4 warriors hitting him with great whirlwind can deal about 1.600 dmg in a single turn (provided that they hit a minimum of 40 dmg per hit, and normally is more, and don't miss any of the 10 attacks).
Comments
Hehehe.
http://www.dotd.com/mm/MM00281.htm
Yes, it is a powerful creature, but NO MATCH for an epic-lv party.
The Tarrasque is ToB would be cakewalk.
In Shadows of Amn on the other hand it would provide sufficient challenge.
Thank you all for listening.