MArcomage

Should be Uncommon (if not Rare)

It can have quite a tremendous effect.

I like the concept. Hard to tell how it would play out in an actual game. Since there is no net loss of resources, it's highly situational. May be severe if used to set up cards that deal damage equal to Resource1-Resource2 (while eating the higher Resource), but in terms of preventing the play of an expensive card, I get the feeling it would only delay the inevitable.

If this were a common, it seems like the kind that would clog up your hand like crazy. Because, really, you'd be pretty silly to play two within a short time frame - the second one would just reverse the effects of the first.

Even if you'd neglect the clogging part, the effect itsself seems to great (potentially) to be common.
If you want to keep it common, cap the switch.

Per recommendations, modified to uncommon rather than common.

Like before, I really like it, and I think the change to Uncommon is a good one.

Now that Earth eater et al are changing, is this card now printable?

Now that Earth eater and company are changing, I no longer have interest in this card.