Eternal Decks · Board game rules
Can I pass a card face down to another player?
Quick answer
Yes — giving a card to a teammate is always done face down, but it costs one Heart (except in Practice Mode).
Details
On your turn, one of the three possible actions is "Give a Card to a Teammate." To do this, you spend one Heart (moving a Heart token from left to right) and give any card from your hand to any other player, face down [p.17 — Give a Card to a Teammate]. This means the receiving player does not see what the card is until they look at it themselves.
If you have no unspent Hearts left, you cannot perform this action, since spending a Heart is required. Certain effects can restore spent Hearts, such as the Skeleton Ability Card (recovers 1 Heart) or the 4th Lap Bonus in the middle Field row (recovers all spent Hearts) [p.17 — Give a Card to a Teammate].
Watch out: In Practice Mode, Hearts are not spent at all, so you can give cards to teammates as many times as you like without any Heart cost [p.22 — PRACTICE]. Also, in Stage D, Skull Cards cannot be played to the River or used to generate Jewels, but they can still be given to another player by spending a Heart if all your cards in hand are Skull Cards [p.36 — Additional notes about Skull Cards].