§ 357.2 Core Rules PDF (officieel)

In addition, pay any non-standard Cost summed in step 3 in any order. Example: A card reads in part “As an additional cost to play me, kill a friendly unit and discard a unit.” When paying the costs for that card, its controller can pay those two costs in any order; they can kill a friendly unit first and then discard a unit, or they can discard a unit and then kill a friendly unit.