MArcomage

This isn't a weak card by any means: two powerful keywords, some attack and ability to replace a certain deadweight with something potentially useful. But...
In fact, Druid is much better when you just have it in hand and don't play it. This is one of the worst Alliance commons to trigger a keyword (no additional production, almost guaranteed token gain decrease), and there are better Mage commons to play when you use a Mage deck. Plus Druid is too unreliable as a summoner. I generally don't want a Nature card in hand when playing Restoration deck and vice versa.
I'd like to see the ability to summon a Restoration removed and another kind of "healing" aspect added - something like +3R.

Maybe simply mode1 mode2 nature restoration?

Then it would be a summoner, not a replacer. You can't select a card to be replaced and type of summoned card at the same time.

Aha, forgot about that.

Then NEW/NOT NEW would do the trick

No weak. So gut card.

At the one hand, i like that it can summon either a nature or a restoration card and that it cannot be controlled.
In comibnation with spring wood you have a relieable keyword trigger of either restoration and nature, since you have are 9+6/9+6/9+4 common/uncommon/rares nature+restoration cards.
This is almost a chance of 28/43 to have a non-common card, while there is a chance of 13/48 to have a rare one.
And we have to think about the nature cards, each uncommon nature is like a free rare (combine with veteran militia or dreamn shift for full effect), while nature rares are heavy-striking ones (apocalytic rain, all elemental attac etc.)
So all in all, the replacing effect is reliable enough in non-nature or restoration decks, while in restoration or nature decks this card is a wasted slot, since your hand is already flooded with nature or restoration cards. I use it in a Alliance/mage deck with spring wood and ent, and its bringing me most time the game ender via nature trigger or alliance and mage tokens, when it stays on hand.
And, above this, this replaces a card. So, you can swap a useless card with a potential usefull one and you get the draw.

On the other hand, this card has an attack value of 5 for 6 gems, what is somekind low. I would suggest a littly buff like a cost reduction to 5 or an attack increasement to 6, but this changes are just that small that they are not needed to be done.