Dyrman
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Surprise Attack is a perk that allows you to teleport a stack and significantly increase its initiative.
Firstly, it's not a skill, but a perk.
And here is the complete description from the manual:
Surprise Attack
The hero gains the "Teleport" spell with a speed-up effect: the next turn of the creature teleported by this spell comes sooner. You cannot teleport a stack behind fortress walls unless the hero has Skilled Light Magic. When teleporting, the stack moves 0.5 forward on the turn order scale. If the position is already > 0.5, the stack will immediately get a chance to move (in this case, part of the effect is simply lost – it will not be "transferred" to the next turn).
