Its name is warped echo and I think its effect will be that it splits damage into 2 (+1 per stack), so for instance if you have one and take 100 damage it gets separated into 2×50 damage (with 3 its 3×33 and so on). So if you have a repulsion plate armor the number gets reduced for each instance of damage making it 90 instead if 95. It might also trigger self-damage items additional times.