How to fix mirror modifier doing weird things? I had my mesh mirrored correctly at first but then I decided to work on the hand in a different layer (Two) and then copy past it back to layer 1. I then selected both meshes and pressed Ctrl+J to merge the 2 into 1 in object mode. However I forgot to apply the mirror modifier before merging the 2 (not that I thought that would matter) and the mirror modifier disappeared so I go on to connect the hand to the arm in edit mode change back to object mode select all and add another mirror modifier. 

Y axis:



Top view of when morring Y axis:



I've tried all Axis and they all seem to be mirroring weirdly in a diagonal fashion. 

Things I've tried already

I've selected all vertices that run along the center from top to bottom on the Z axis then Pressed Shift+S and selected "Cursor To Selected" followed by Shift+Ctrl+Alt+C selected "Origin to 3D Cursor" and still have the same results.
Is very likely that you have the object rotated in one or more axis. You can do 2 things (as far as I know):


Apply the rotation (keeping the current visual orientation): press, while in object mode, Ctrl+A and then select rotation.


Set the rotation values to 0 (this will rotate the object to a different orientation): in the object properties menu, in the transform tab set all the rotation values to 0.