Keep your alien secret until you use it

Fantasy Flight's Hidden Powers variant, from the core rulebook. During setup nobody reveals their chosen alien sheet — the sheets stay facedown and the flare cards are shuffled into the cosmic deck without being shown. A facedown power cannot be used; a player may turn their sheet faceup at any moment in order to use it, and once faceup it stays faceup for the rest of the game. The standard game reveals every alien at setup, so the table knows from the first encounter what it is up against; this hands each player one surprise and makes the choice of when to spend it part of the game.