cr:4.1.5b

If a meta-static ability effect allows the player to start the game with one or more cards in a zone other than their deck, these cards are selected from their deck and placed face-down in their respective zones or in the single face-down pile next to the hero. The cards selected this way are still considered part of the player’s deck. These cards and their number are private to each player until the game begins.

Example: Dash has the text “You may start the game with a Mechanologist item with cost {r}{r} or less in the arena,” which means if the game format requires a starting deck of 40 cards, the player may select the specified from those 40 cards, and start the game with 1 card in the arena and 39 cards in their deck zone.