It's easyer than it look:
The game start with the following variable "scaleHp".
On default this variable is globaly set to 1 and in most levels this value is modified.
Some examples:
Campaign Level 1-1[]
Wave 1:
- scaleHp[Global] = 1
Wave 2:
- scaleHp = 0.5
Wave 3:
- scaleHp[Global] = 1
- last skully: (unknown action that set his hp to 120, scaling hp should 1.5)
Campaign Level 1-2[]
Wave 1:
- scaleHp[Global] = 1
Wave 2:
- scaleHp[Global] = 0.7
Wave 3:
- scaleHp[Global] = 0.7
- last skully // scaleHp = 2