This video shows how to kill in Spartacus Legends, the game’s version of a Mortal Kombat fatality. You should also gain the Vidi Vici Veni achievement/Trophy.
Firstly you MUST choose the “Boost” option before the fight begins to enable the execution move. Select the first option of whatever allows you to perform a finishing move. The first card costs 500 silver and allows for the Face Carver finisher. Purchase and equip this.
During the fight build up your crowd meter as seen on the top left of the screen. Simply land blows, taunt (use te d-pad when at range from your opponent).
In the closing stages of the fight make sure to stagger the opponent by not raining down too many flurries of moves. Then when the opponent is groggy simply move close and hold the hard or weak attack button to finish him.