Reef Madness features the battle for survival between predator and prey. One player takes on the role of the fish, who is trying to navigate the ever-shifting reef and escape the shark. Meanwhile, the other player endeavors to find the shark its next meal. The game plays out on a 5x5 grid made of double-sided cards, with one additional card. On a player's turn, first the reef must be shifted. The player chooses any row or column that wasn't just shifted by the other player and doesn't contain any player tokens. All the cards in the selected row or column are moved by one space in the grid, thus changing the map layout. After shifting the reef, the player moves according to the rules for their role. The fish player wins if they can move across the reef and move off the shark player's map edge, while the shark player claims victory if they can land on or move over the fish player's token.