According to the report Mortal Kombat "contains violence that exceeds strong in impact and is therefore unsuitable for persons aged under 18 years to play."
As you'd expect - the fatalities were to blame.
At the conclusion of a bout, a character is invited to perform a 'finishing move' or 'fatality'. To perform a fatality, a player has to push a series of button combinations within a short period of time. If this is successfully accomplished, a non-interactive cut scene is triggered which depicts a character explicitly slaughtering their opponent.
Initially, the Move List Within the game includes one finishing move per character, although a player is able to unlock up to four per character. The Board notes that fatalities cannot be performed in Story mode and are unlikely to be performed frequently during gameplay; however, it is also noted that there are more than 60 fatalities available and they are an important component of the game.
The report then goes on to describe some of the fatalities in detail...
- Stryker tasers his opponents and then explicitly shoots their head off with his gun. Blood and gore is noted.
- Shao Khan uses his hands to explicitly rip an opponent's body vertically in two
- Kitana uses her 'folding fan' weapon to explicitly dismember then decapitate her opponent, with copious blood flow noted.
These fatalities are then cited as being one of the major reasons why Mortal Kombat has been Refused Classification.
The game includes over 60 fatalities (some of which are noted above) which contain explicit depictions of dismemberment, decapitation, disembowelment and other brutal forms of slaughter. Despite the exaggerated conceptual nature of the fatalities and their context within a fighting game set in a fantasy realm, impact is heightened by the use of graphics which are realistically rendered and very detailed. In the opinion of the Board, the game contains violence that exceeds strong in impact and is unsuitable for a minor to see or play. The game should therefore be Refused Classification pursuant to item 1(d) of the computer games table of the National Classification Board.