Hearthpwn

I love your thinking but that's not it. In fact, the card has nothing to do with Un'Goro.

Alright, well then, let's take a run at Unstable Portal.

Babbling Book

It was Unstable Portal, you're up JibbaNerds.

//Well, from where I'm sitting, it looks simple enough, but I'm sure we'll see.

If you're searching for something
That you know that you've got,
And you need it right now,
I can help you a lot.

But my power, of course,
comes at too great a price
So unless you get ready
I'll lose you the fight.

And what's the last strike?
Made me the simplest target?
Let me tell it now this way
I lost out at the market.

Let's analyze this poem.

If you're searching for something
That you know that you've got,
And you need it right now,
I can help you a lot.

This sounds like the card can tutor something out of your deck. The most obvious example of this would be Shadow Visions.

But my power, of course,
comes at too great a price
So unless you get ready
I'll lose you the fight.

The card also has to have some sort of drawback that could even lose you the game if you're not prepared. Temporus comes to mind but he doesn't tutor you any cards.

And what's the last strike?
Made me the simplest target?
Let me tell it now this way
I lost out at the market.

About this one I honestly don't know, but it seems like just bonus tips. Could be a reference to a voice line or flavor text.

Overall, a card with a big drawback that can be used to fetch something specific out of your deck. Can't figure it out right now but maybe this'll help other people.

I feel like you are going for Aluneth.

The card can draw you cards quickly to help you get what you need, if you aren't prepared for the effect, it can cost you the game, and far as I can make out for the last part is you are stating it lost out at the market because it is too greedy in some cases.

Just my shot in the dark man.

You know, that's an excellent answer, and most of your logic went down the same paths as mine, but it was incorrect.  I'd recommend finding a slightly more direct interpretation of the third stanza.  However, with an answer that close, I'll narrow things down a bit further.  Finally, you're using a word that I was directly referencing in the clue, which, if you thought about it, would lead you directly back to this card.

By the mana, I'm costly,
and for tempo, I'll cost ye'
but you'll have me quite cheaply,
I'd bet cash that you've got me.

Gadgetzan Auctioneer?

You're on the right track.

I honestly don't know, maybe Starving Buzzard?

Also, reviving this thread.

Y'know what?  I'll take that.  It has the tempo loss, and it's understatted.  It's a lot of draw, and never played because of better options.  I was actually going for Sprint, which, is much alike, and as I was hinting at, is a basic card.  I was thinking of Gadgetzan Auctioneer, which was often run in Rogue for draw, but only as part of the clue.

Over to you.

I am a miserable soul of emotions,
My anger, like billions of oceans,
Swarms through all of my rivals.
But when the agonizing finals
Come, I will simply be no more.
No more will I see 1/1's at war,
No more will I strike at a jam.
Lastly, my favourite band is Wham!

Should be pretty easy for all of you.

No, although I'm actually quite surpised to see how well this card fits into my riddle.

I'm guessing Onyxia.

Ticking Abomination

Nope and nope.

Hint: it's not a minion.

Spreading Plague

If its not a minion, (due to the mention of 'strike' and 'wham')  I'm assuming it has to do with a weapon. I first think of Vinecleaver since it summons the recruits. 

Next I think of Widow's Bite since it clears anything with 1 Health when it dies. 

 lastly I think of Uther of the Ebon Blade since he equips a weapon and no loner summons 1/1's with his hero power.