Only you will see this mod, your opponent can't see it.
To install go to "C:\Program Files (x86)\Steam\steamapps\common\Yu-Gi-Oh!
Master Duel\LocalData\SomethingSomething\0000\34" or where
you installed the game , you can also go there by rightclicking the game in
your steam library and selecting browse local files. Then drop the file "343fe86c"
in that folder replace the existing one, just make sure to back
up the one you're replacing in case you wanna go back
To install go to "C:\Program Files (x86)\Steam\steamapps\common\Yu-Gi-Oh!
Master Duel\LocalData\SomethingSomething\0000\34" or where
you installed the game , you can also go there by rightclicking the game in
your steam library and selecting browse local files. Then drop the file "343fe86c"
in that folder replace the existing one, just make sure to back
up the one you're replacing in case you wanna go back