OK, we're all agreed, then.
Tactics: As a divine messenger, a grandfather-of-all-turtles usually confronts threats indirectly, through allied adventurers or perhaps with the use of control weather. In direct combat, a grandfather-of-all-turtles summons chelonian allies or attempts to swallow opponents whole.
I'd rather not mention the "divine messenger" bit in the tactics.
How about this...
A grandfather-of-all-the-turtles is a legendary reptile that some cultures considered a sacred beast. They live in both fresh and salt water, unlike the purely marine father-of-all-the-turtles. Grandfathers-of-all-the-turtles can fly and travel the planes at will, so one may appear in any lake or sea, or even a small pond. These turtles can eat the same aquatic plants and animals as normal giant turtles but prefer to obtain their food magically via their
heroes' feast spell-like ability.
Folklore says this mysterious creature is either the avatar of a "Turtle God" or a father-of-all-the-turtles of such vast wisdom it transcended its animal origins. What is certain is grandfathers-of-all-the-turtles sometimes serve as intermediaries between Material Plane people and divine beings such as deities or dragon rulers. Some other grandfather-of-all-the-turtles serve as guardians of aquatic life, particularly turtles.
When not performing some task for nature or the gods, most grandfathers-of-all-the-turtles are extremely shy and furtive. They avoid interacting with humanoids but may watch them secretly, either by shrinking to Diminutive size and hiding or
plane shifting to observe from the Ethereal Plane.
Grandfathers-of-all-the-turtles do not value treasure, but do occasionally have treasure given to them by a divine patron to deliver to a chosen mortal (or protect until a worthy owner appears). Such divine treasures are often powerful magic items or even artifacts, and some have served as the foundation relic of a dynasty or religion. The turtle may return to retrieve its patron's gift once the treasure's time on earth is done.
There are reports that some of these creatures possess additional powers. Known examples include breath weapons, transporting incredible loads (in one case, flying while carrying a small island), producing earthquakes, regeneration, the ability to grant
wishes to small children, having alternate forms (usually a normal-sized humanoid or an enormous tortle), or the power to store and retrieve items from an extradimensional "strongbox". A grandfather-of-all-the-turtles with a divine patron may by temporarily endowed with a power to fulfill a task or duty, but most such powers are innate abilities.
A grandfather-of-all-the-turtles typically measures from 40 to 60 feet from snout to tail, with a shell from 30 to 50 feet in diameter, and weighs 120 tons or more. The oldest individuals grow to length of 100 feet or more.
Can these things speak? If so, what languages do they have?
COMBAT
Grandfathers-of-all-the-turtles normally only fight if the situation is vital; they would rather fly, swim, or
plane shift away from threats. Given time, they use
control weather and
summon chelonians to gather allies and change the environment in their favor.
A grandfather-of-all-the-turtle's battle tactics are pretty straightforward. It uses change size, flight and/or plane shift to get within melee range of their opponents then attack with its bite. Smaller opponents may be swallowed whole, but only if the turtle judges them too weak to injure it internally. Enemy spellcasters will be countered by
greater dispel magic (quickened when necessary).
Grandfathers-of-all-the-turtles routinely apply their
arcane sight,
heroes' feast,
true seeing and
water breathing spell-like abilities to themselves. Remember the
heroes' feast grants them 1d8+10 temporary hit points, immunity to poison and fear effects, and a +1 morale bonus on attack rolls and Will saves.