MArcomage

Well, I recently built a Charge deck and I would call this card the main part of the deck just because it has extremely narrow summon list.
It can summon two commons, Warhound and Knight - cheap way to raise Soldier tokens.
It can summon Light and Heavy cavalry - pretty good cards by themselves.
And finally it can summon Royal dragoons and Imperial army. First one is 25 + 8N + 15 attack. This usually means 88-104 attack, depending on how many Charge cards you have. Second one is straightforward 90-95 attack - or 45-55 plus basically -15 enemy stock if enemy raised his wall above 45.
I don't want to nerf it by any means, but it needs more common and uncommon Soldier/Charge cards to make its summon effect slightly less predictable. For example, Paladin can get Charge(5) and Lancer can be returned to Soldier cardset with slight rebalance and Charge keyword. Also, there are some Soldier/Charge concepts...

Shameless bump.
As you can see, my Charge deck has >3 win/lose ratio. And I'd say this deck won more Assissin awards than any other deck of mine, mostly because if I didn't draw Royal dragoons as part of my starting hand, I always have 1-2 tries to draw it with Stables (remember, it's 33.(3)% that you'll get a jackpot with this card, if you count Imperial army).

Why non rare?I think its unfair compared with other summoning cards

It's balanced this way for its low cost as a Common card.

Mage guild and schools of nature and restoration also the druid are all low cost commons but they can summon rare cards...

Well, the reason is because there are so many rare charge cards. I believe it was debuffed because the set of cards it summons was so stron.

In particuallar, stables have a 100% chance to summon an offensive card. The keyword itself is aggresive, so every card summoned will fit into an agresive strategy. Compared to the other ones, mage guild andthe schools have so mixed card set that sometimes it should be considered to not be put in your deck (School of restoration should in my oppinion is particular weak).

And if you would read the comments above, that were the reason why "non-rare" was added. But i suspect that you didnt.

Your description of mage guild has been of great assistance:3 I will need to rewrite a few card concepts.
Thank you very much<3