This is a 3 coin set, with 2 of the coins being bonded together and the 3rd coins mated to the other two coins, but having separated after strike. The double-strike fits perfectly into the other two coins on the reverse side.
The error occurred when the three coins were struck into each other multiple times, bonding two of them together, although the 3rd coin simply separated but still "mated" with the other 2 coins. Bonded coins are quite scarce, and are universally considered to be one of the most dramatic error types.
NGC MS-65 Red/Brown for the mated coin, and MS-66 Red/Brown for the 2 coin bonded set.