Ryse: Son of Rome Wiki
Once an enemy is sufficiently injured (which is noted by a skull above their head), you can perform an execution by pushing R2. When you enter the execution mode, time slows down and the enemy flashes blue or yellow at specific times; pushing the corresponding button (X or Y, respectively) will take Marius through a predetermined set of actions. Timing the button presses perfectly will get you bonuses – timing ratings of Recruit, Soldier, Centurion, and Legendary determine the quality of execution. Expertly-timed combos lead to better executions, which leads to more Valor points to spend upgrading Marius’ stats and executions.
It should be noted that even if the player misses a button – hitting Y instead of X, for example – the execution is still carried out, the bonus payout is just not at great.
Combos and executions during battle reward perks. Perks can be selected using the directional pad on the controller. After each execution perks replenish health, amplify damage, refill focus, or multiply XP.