Discarding Cards
From Archon Arcana - The KeyForge Wiki
The active player can discard from their hand any number of cards belonging to the active house during step 3 of their turn. When a card is discarded, it is placed faceup on top of its owner’s discard pile.
Unless otherwise specified, when an ability refers to a player discarding a card, the discarded card must come from that player’s hand.
If an ability requires a player to discard multiple cards from either their hand or the top of their deck, the cards are discarded one
at a time. If an ability requires both players to discard multiple cards from either their hand or the top of their deck, the active
player decides which player will discard first. Once that player has finished discarding cards, the other player discards cards.
—KeyForge Master Rulebook v17.4 September 2024