I have a small suggestion; keep it in line with Faceless, and give it an effect based on the card it copies. For instance:
If the copied card cost is X, then Y.
X: bricks, Y: Attack: 10
X: gems, Y: Stock: +2
X: recruits, Y: Wall: +10
X: mixed, Y: Tower +5
which meshes even better with Far Sight (which can have trouble vs. gem decks), or
Gain N/4 random tower, wall, or resources, where N = copied card cost.
which is straightforward and hasn't quite been done, or perhaps even
Trigger non-summoning, non-Durable/Cursed, keyword effects of the copied card as though Shapeshifter had those keywords.
which if implemented would make the card quite good on Quick/Swift cards (and also be the only way to trigger Uncommon Flare Blitz but I'm not sure anyone cares).
It seems like Shapeshifter has the potential to do something more clever or interesting than just another keyword.