It's a HUGE buff for offensive decks of any kind. Personally I don't like it, but I'd deal with a common like this, if it wouldn't reduce enemy stock against non-offensive decks.
Pixie has similar effect, yes, but there's one very important difference. Pixie is based on current hand rarity which isn't constant. You are in "common pit", enemy just played Scepter of Evolution or big Illusion chain - it will hurt him or at least will not affect. Pixie can be a common without any big issues. But this one is based on cards you (and your opponent) have in your deck - and it's definitely power level of an uncommon, like Moon shrine and Moon castle. You cat get rid of uncommons and rares if you need it (Wish, for example), but you can't make your deck keywordless, zero-cost or offensive to at least avoid these cards' effect or turn it into a double-edged sword.
So either make it uncommon without changes or remove stock reduction completely - and it will be fine.