Simply enough, Unit cards are the units that fight your opponent. They have attack and defence values similar to other card games and when their defence drops to 0 the unit goes into the Discard Pile. Each unit has a specific number of slots that can be filled with attachments to enhance the unit. Any attachment can be replaced, moving the previous attachment to the discard pile.
Attachment cards can be attached to slots on Unit cards. The key word will become the unit’s effect, for example, Shield generator provides a unit with “Force Field” permanently which absorbs full damage once. The colour of the attachment and the colour of a used slot decides how many faction points are awarded. For more on faction points, see the How do I get synergy effects? page. Units keep their attachments for the whole game, even when they go to the discard pile.
Power cards like Hallucination from Incense can be thought of as a spell card. However, Serra is a sci-fi world without magic. This card’s power for example is time travelling, enabling complex strategies alongside more traditional heal, damage or buff Power cards.