Пока что вроде ничего нет...Хотя я сильно не искал.).
Вот,к примеру,люди рассуждают и делают попытки -
green dragon: HP 200 -> 150, gold 3000 -> 2000
red dragon: HP 250 -> 175, gold 3500 -> 2500
black dragon: HP 300 -> 200, gold 4000 -> 3000

giant: no change
titan: HP 300 -> 200, gold 5000 -> 4000

Now some maths on gold costs. The total "power" of a creature is proportional to SQRT(HP*damage), so if a creature has 2/3 of its original HP, its power is SQRT(2/3) of what it was. This means that if you want to keep the original theoretical cost/effectiveness equal, the HP above would correspond to the following gold costs:

green dragon: 2598 gold
red dragon: 2928 gold
black dragon: 3266 gold
titan: 4082 gold
Тут