I’ve created a character plus armature.
But i’ve done something wrong along the way,
and my character deforms in mirror.
When I move my right armature the left one deforms and the other way around.
It’s probably something very simple, I can’t figure out how to undo it
In general, it’s better to reset (apply, whatever) the scale of a model before any kind of painting or sculpting. That, of course, includes weight painting. If you applied weights via auto-weight, the same caveats apply, too.
One way to do a quick fix on this would be…
of coarse apply your Scaling and Rotation… (just as Ovnuniarchos recomends)
once you do this you will find that all your polygons have been flipped…
Tab into edit mode…
hit ‘A’ to select all faces > Find Mesh (on the bottom tool bar) > Normals > Recalculate Outside
hit ‘A’ to unselect all your faces/vertices…
Now goto Vertex Groups…
Properties Panel > Object Data (triangle Icon) > Vertex Groups…
here you will see a list of all your vertex groups that got created when you did your Ctrl+P automatic weights…
select any one of these Vertex Groups and then hit the ‘select’ button at the bottom of the list…
you will see all the vertices that this Group has influence on…
So now select Shoulder.L and hit select and you will see that Shoulder.L actually is controlling the Right Shoulder area and not the Left Shoulder area…
a simple fix is to simply rename that Vertex Group to Should.R…
as Blenders Armature scheme keys on the name of the Vertex Group that matches the name of the bone…
Change the name of the Vertex Group to match a different bone and you can now pass control to that bone…
Note that Blender won’t let you just Rename over a name that already exist so when you try to Rename Should.L to Shoulder.R it will actually rename it Shoulder.R.001 not to worry… just leave it like that until you rename Shoulder.R to Shoulder.L and then go back to Shoulder.R.001 and rename it Shoulder.R and it will work now…