Simple question: Can I kneel a Summer/Winter Reserves with my Harry the Riverlands?
Card text: House Lannister only.
Any Phase: Kneel any number of characters with combined printed cost 3 or lower.
Argument for yes: The Reserves are a character, and thus are a valid target. For the purposes of adding up the cost, its cost is 0. (Card doesn't specify that you can only kneel characters that have a printed cost; FAQ (3.1): Further, any card without a cost of the specified type is assumed to have a cost of 0 for purposes of determining how that card interacts with triggered effects that need to count its cost.)
Argument for no: The Reserves do not have a printed cost, and thus are not a valid target. (That the knelt character(s) need to have a printed cost is implied by the wording: "Kneel ... characters with ... printed cost"; Impossible to add up the combined printed cost of the characters when one of the values for printed cost is "null", FAQ (4.19): Printed Any reference made to "printed" be it cost, STR, icons, etc. only refers to the referenced item physically printed on the card itself. A card like Summer Reserves (Scattered ArmiesF119) does not have a printed cost or STR for instance. Any card effect that looked for the printed cost of a card without a printed cost would fail to find any cost and would return a null value, no item that could be referenced.)
I find both arguments have merit (we had no idea how to resolve it). I lean towards yes, but it seems to very much come down to a semantic argument of whether the event thinks it can kneel characters without a printed cost, and the wording is ambiguous at best.