"Mortal Kombat" further introduced the concept of "juggling", knocking an opponent into the air and following up with a combination of attacks while the enemy is still airborne and defenseless. The idea became so popular that it has spread to many other games. Another of the game's innovations was the Fatality, a finishing move executed against a defeated opponent to kill them in a gruesome fashion. In the single-player game, the player faces each of the seven playable characters in a series of one-on-one matches against computer-controlled opponents, ending in a "Mirror Match" against a duplicate of the player's chosen character. The player must then fight in three endurance matches, each of which involves two opponents. As soon as the player defeats the first opponent, the second one enters the arena and the timer resets; however, the player's health meter does not regenerate. After the third endurance match, the player fights the sub-boss Goro, followed by a final match against Shang Tsung. Between certain levels, players can compete in a minigame called "Test Your Might" for bonus points, breaking blocks of various materials by filling a meter past a certain point through rapid button presses. The first material the player must break is wood, followed by stone, steel, ruby, and finally diamond, with each successive material requiring more of the meter to be filled up and thus awarding more points. Two players can compete in the minigame at once and the last two materials are only accessible through two-player mode. The minigame would return in various forms in "", "", "Mortal Kombat vs. DC Universe", and "". The game takes place in Earthrealm, where a tournament is being held on Shang Tsung's Island, on which seven of its locations serve as stages in the game. The introduction to "Mortal Kombat II" explains that Shang Tsung was banished to Earthrealm 500 years previously and, with the help of the monstrous Goro, is able to seize control of the Mortal Kombat tournament in an attempt to doom the realm. For 500 years straight, Goro has been undefeated in the tournament, and now a new generation of warriors must challenge him. The player receives information about the characters in biographies displayed during the attract mode. The bulk of the game's backstory and lore was only told in a comic book, but some additional information about the characters and their motivations for entering the tournament is received upon completion of the game with each character.