Reserves: , Pay 1 Force Choose one of your units with Upkeep. You do not have to pay the Upkeep costs of that unit this turn. Play only when your build step starts.
Keywords
Reserves
Reserves: [Ability]: A layered, static ability that means, "The following ability works while, and only while, it's in the build zone." The granted ability remains to be the ability of its type. (For example, activated abilities granted by Reserves may be disrupted.)
Upkeep
Upkeep: [Cost]: A layered ability triggered when the build step starts that means, "When the build step starts each turn, you must pay the following cost." You must choose one of the costs that you can pay each turn, and ignore the others. You must still pay the Upkeep costs of a unit even if that unit is in the build zone, becomes the top card of a unique unit stack, or Pilots another unit. The Upkeep must be paid if you can pay it. If you can't pay any of the listed costs in full, then ignore Upkeep. If a unit has multiple Upkeep abilities, fulfilling just one of the Upkeep abilities (such as tapping the unit) does not satisfy all the Upkeep costs at once; it would only satisfy that instance of Upkeep. You may choose the order of multiple Upkeep abilities to keep an Upkeep from being paid, though a different order might pay it.