This card appeared in the Yu-Gi-Oh! movie based on season 0, the original Yu-Gi-Oh! series that only aired in Japan. It is, in effect, the original "Blue-Eyes Ultimate Dragon" and was probably the inspiration for it.
While there is no formula to how the 3 Blue-Eyes joined's ATK and DEF is calculated, one can assume the ATK is equal to the combined ATK of all 3 monsters, then divided by 2. The DEF could just be equal to the ATK of one of the 3 monsters.
Due to the Special Rule printed on this card, this is the only card that can attack 8 times in a row.