Just got the Lugia v alternate art from silver tempest and cant put in any decks why is that.

Whitesox35

DragonVen0m

In deck editor, did you go to Lugia V? It should only show one version. Click on that card. It will have a drop-down menu underneath that. Then you should see the alternate v art.

StelLamp

This method also works for every other alternate rarity card you have btw.