Colossal dragon bite: 4d8
improved natural attack: 6d8
strong jaw: 12d8
all vital strike feats: 48d8
Since many dragons can cast from the cleric spell list, they could also cast righteous might to get to 64d8
Does anything not stack or is anything miscalculated???
(and for damage, this is all +1.5 strength + power attack . . .)