MArcomage

This is too powerful to have such a low cost and be a common card.
The stock will always be raised by at least 3-4 (which gives you back any resources you spent) and also it gives you immediately a rare card. You could make this an uncommon card and limit the stock increase or increase its value

I don't think Legends should be targetable for summons by any card, let alone an inexpensive Common.

This card, as it is now, would be overpowered for a Rare.

First, I meant to make it an uncommon. It's changed.
Second, it's only a stock-booster with no other benefit. You can get lots of stock using other cards (see Timewarp, Farie, etc.)
Third, Legend is not the same thing as rare (see Azure unicorn, Moonlight unicorn, Frost unicorn). However, I've changed it a little.

It's still too powerful.

A legend can very easily win the game for you. If you are able to summon it from such an inexpensive card then everyone will have it in their decks and a match will last up to 10-15 rounds

I disagree with that... Sure, legends are good, but the non-rare ones are expensive.

I think you should just leave the cost boosting effect

Maybe. But Moj is the final say and can tweak if necessary.