I encounter a lot of decks that simply play for this combo. I play a paladin control deck and I've practically lost already when a mage is able to play this combo.
I feel very unfortunate if such a combo happens, I mean, 50% chance of having the coin, and a significantly smaller chance of having wyrm+image. Also, it has to be starter hand cause it sucks in mid- or late game.
I don't see the point in creating a deck with that purpose. Most of the games you're not able to play that combo and only in early game it's actually usefull. Midgame any deck has enough resources to remove at least the wyrm.
At least one aspect of this combo deserves a nerf imo. The coin is quite balanced and if importance to game balance in general. So either nerf the wyrm, or mirror image.
I'd go for image. Early game, you need 4 instances of dmg to remove them, since most decks aren't able to play 1/1+ in the first 2 turns, let alone boardwide removal.
Either make it summon 1 x 0/2 minion or reduce the hp to 2 x 0/1.