Reflective Shield is absurd because it renders decks reliant on damage spells completely worthless; this single card can discredit an entire category of strategies in this way.
How to fix: Remove "cannot be destroyed or stolen" flag. While it would still serve its purpose, that is, as an anti-spell shield, and it is still a threat to users of spell-reliant decks, it's no longer an insurmountable wall of death to these decks.
I think that's the point though; against decks based SOLELY on spells, not having any type of reflective/emerald shield to defend against bolting strategies is a bad concept in general, and would ultimately tip the meta into a boring direction that revolves around saving up quanta, then bolting (or exploding, if you like Unstable Gas) away until the enemy is decimated. Firestall was nerfed for this very reason with quanta caps (although it didn't work as well, seeing as Ice Bolt/Drain Life were affected more), and to me, I don't think it Reflective Shield should be nerfed for that reason at all.
If anything, a shield that would stop ALL spells (not just damaging spells like Lightning and Fire Lance; but things like silence, blessing, reverse time, and earthquake) would be much more nerf worthy in a thread, but alas, the reflective shield doesn't deal with those types of spells...