As XtremeCharizard said, we can't really tell you, but this is their stats combined and then taken the average of the combined stats

**HP**- remains **125** since Kyurem's HP will not suddenly decrease because eit is combined with Reshiram and Zekrom

**Attack**- would become a base **133** which is **401**(.3333..) at max

**Defence**-would become a base **103** which would be **335** at max

**Special Attack**-would become a base **133** which would be **401** at max

**Special defense**- would become a base **103** which would be **335** at max

**Speed**- would become a base **95** which would be **317** at max

These are just the averages and together they would make him have a base 692 stat.

*Another variation will be added quickly*