VISUALIZING ALL THE TIME
Here you can see an attempt to categorize all angels and monsters. This is information that the player doesn't necessarily see. It's just a guide for myself to get a clear line into the active and passive skills. There are skills that are clearly on the angels side and skills that are clearly better suited to demons. For example, increasing range of motion is more appropriate for Angels and direct damage is more appropriate for Demons.
To give the game some consistency in the asymmetry, the skills are strictly separated for level 1 and 2 Angels and Demons (12 out of 16 monsters). For level 3 Angels and Demons (4 out of 12 monsters), the skill separation blurs to emphasize the special power of these creatures and give the system a small edge.
After that I started to develop a system for the skill cards that makes also use of this skill mix:
The games engine are 5 different Decks: The Armageddon Clock, the Battle Card Deck, the Digging Deck, the Resource Deck, and the Quest Deck. When a player plays a skill, the cost is simply where the card is discarded. There are, so to speak, 3 cost levels, measured by the accessibility of the card after discarding: