An interesting idea, but now there is way too few permanents for this to be worth it. But it seems you have some other permanent damage card planned, so together they might very well work good.
How about making the unupped go randomly on the field and the upped randomly on opponent field, like pandemonium?
I like the idea, but fully negating weapon damage seems a bit too powerful... decks like Poison dials Sosac have their effectiveness reduced dramatically.Also, will this potentially allow you to bypass spell damage shields if you cast Catapult on yourself with this shield up?