Scáthach temporarily summons a massive gate to her shadow realm, and it sucks in all life forms in range. If the target fails to resist it with one's Mana or Luck stat, they're sucked into the gate and are instantly killed. Scathach can choose specific targets on whether to allow them access or not. Even if resisted, the targets' mana is rapidly drained and they take major damage.
In the events of Fate/Grand Order during the North America Singularity, she attempts to forcibly send Cú Chulainn Alter to the Land of Shadows with it, but fails as he retaliates. However, she was able to escape from him by going through the gate and hide herself in the Land of Shadows until she recovers.
- ↑ 1.0 1.1 1.2 1.3 1.4 Fate/Grand Order Material Book II: section on Scáthach's Gate of Skye Noble Phantasm, translated by mewarmo990 at Beast's Lair.