What rarity is this?

Uncommon, but likely it's no good fit for a given set.

High ward costs just go wherever hexproof goes.

You forgot "Pay" and a comma. Compare: Garza's Assassin.

I'm skeptic whether "you" will ever be used in a ward cost given how confusing it could be whether it refers to the player paying the cost or the controller of the card (though there are clearly distinguishable wordings for each case; players will still have issues telling them apart if they are not next to each other).