204.1. Base Costs: These costs are the most fundamental costs that must be paid to finalize a card or ability.

204.2. Additional Costs: These Costs are in addition to the base cost of the card or ability and will include "as an additional cost."

204.3. Costs within Instructions: These Costs are part of the resolution of a spell or ability, and will take the form "[do X] to [do Y]."

204.4. Applied Costs: These Costs are applied to one or more Game Actions, and typically take the form of a passive ability with a Cost within Instructions preceded by "must." Example: Mageseeker Investigator reads in part "Opponents must pay [A] for each unit beyond the first to move multiple units to my battlefield at the same time." This is an applied cost.