Rifts have two effects. First, a player may play a rift to receive a benefit of ships, cards, or a colony as stated on the card. Additionally, if a rift card is taken from a player's hand and kept, either as compensation or as the result of another game effect, the rift detonates, causing the theiving player to lose ships, cards, or a acolony as stated on the card. After detonating, a rift is discarded. Rift cards can only be round in the Reward Deck. Because the reward deck has different back art, it is easy to tell if a player has these cards in hand. Many are desirable cards, so they are often targeted for compensation, but the possible presence of a rift card can act as a deterrant.
Cosmic Incursion's reward deck contains Rift cards that only affect ships (3, 4, 5).
Cosmic Dominion added the Rift cards that gain/lose cards and colony (2 and 1).