During combat only one of the six tiers is active at any time. Combat always starts at the first tier. When a skill is executed the next tier becomes active and so on until a skill is used from the last (sixth) tier, in which case the first tier becomes active again. The time it takes before the next tier becomes activated (and thus when the next skill can be executed) depends on which skill was used and the current attack speed of the character. To execute a skill, the player selects it with the number (1 to 5) keys (this is similar to selecting a weapon in a first person shooter game) and then uses the skill with a press of their mouse button. Once used, the skill takes effect in the area where the player is aiming.
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