Looks like we will have the thunder dragon after the flame and water dragon,
Compare to Wales and Prothero, thunder dragon's HP and defence are in between the two. Its HP is about 35% of Wales and its defence is a lot less than Prothero. You can always bring a defence ruin to maximize your attack output.
Its atk is about 1.7 times more than Wales and it's 2 CD. Its skills are unknown for the moment.