When an ability instructs you to play a card from a zone other than your hand, do you have to pay its cost?

Ruling: Yes, you must pay the full cost of the card unless the ability explicitly states otherwise. Riftbound uses the principle that costs must be paid when playing cards, and only abilities that include phrases like "ignoring its cost" or "play it for [cost]" allow you to bypass the normal cost.

Nuances:

• This applies to abilities like Rek'Sai, Swarm Queen's "When I attack" ability that instructs you to play a card from the top of your deck.
• Any mandatory additional costs (such as those from keywords or passive abilities) would still apply even if the base cost were ignored.