copying mask and pasting edits whole thing

Cropped screenshots don't tell the whole story and we simply cannot know what's going on. As Rick already pointed out, most likely you have simply transformed the layer in some way and not considered that mask coordinates are relative to the layer, not the comp. Beyond that obvious statement we really can't tell you more until you provide better info.

Mylenium

Mask Position is based entirely on Layer dimensions. You have scaled, rotated, or moved the layer with the mask. Transform the layer, and a copied mask will not end up in the same place on another layer. Neither will the motion path.

If we saw a screenshot with the modified properties of the source layer and the target layer revealed, we may be able to present a workaround. 

for context, im doing the saber effect on a gun in valorant. you have to put the saber effect and mask on the same layer/shape so the saber can gp onto the path.