Three-of-a-Kind is the name of a group of enemies from The Legend of Zelda: Link's Awakening. These small, round enemies are usually the only monsters located in the room in which they are found. They must be defeated in a most unusual fashion for Link to solve the puzzle in the room: the symbols on the monsters constantly revolve between a Club, Heart, Spade or Diamond symbol.
Once Link attacks one, it will be stunned and the symbol will be set to whatever was the last symbol displayed before it was attacked. If Link manages to make all the enemies' symbols the same, a process that requires precise timing, they will be "defeated" and Link will be able to pass. If Link fails to get all the symbols correctly, they will reset and Link will have to repeat the process.
A clever way to beat this puzzle easily is to hit at least two with a Spin Attack if the revolution of the symbols are in perfect synchronization. This will cause the two to stop at the exact same symbol. However, if one fails to do so, the revolution will become unsynchronized again, forcing Link to leave the room or manually restore synchronization by hitting them. If all three are hit while showing a Heart symbol, they yield hearts upon "defeat"; if they are all hit with a Diamond symbol, they yield three Rupees.
"Three of a kind" is the name of a variant of cards that can be achieved while playing the card game, poker. In order to get a "three of a kind", one must get a match of the same symbol of card, either a Club, Heart, Spade or Diamond, on three of the five cards drawn.