Royal 21 is a follow-up to FURY's Vector 21, the first ever card game for the Vectrex. From its predecesor, a Tetris element was added, where dealt cards advance towards the playfield area and the player has to move them to the appropriate stacks (note: unlike with Tetris though, the cards move from the bottom to the top of the screen, rather than top to bottom). The object is to get as many cards as possible in a stack to equal 21 or to have five cards in a stack equal less than 21, which will then remove the stack from the game. A stack can only have five cards maximum; if a fifth card is placed in a stack and the stack amount is over 21, then that stack is a bust. There are four stacks from left to right on the screen, although they are not numbered. (The first stack is at the left side of the screen, the one next to it on the right is the second stack, etc.)