A fighter can make this reaction after an enemy fighter finishes a move action visible to this fighter and within 3" of this fighter. Pick another friendly fighter with the Gloomspite Gitz runemark. That fighter makes a bonus move action. After that move action, that fighter must be within 1" of the enemy fighter that made the move action.
Building an army? Create, validate and share your list with New Recruit, army builder for Warhammer Age of Sigmar: Warcry and many more games.
Try the builder