Hearthpwn

Even setting aside the obvious synergy with Scavenging Hyena or the DK Rexxar Zombeast shenanigans Echo allows you to do, I find myself enamored with Hunting Mastiff for the fact that it's a 2-cost minion that doesn't really lose its value over the course of the duel thanks to its Echo/Rush mechanics. On the contrary, it "grows" in "power" at turns 3, 5, 7, and 9, and can be a lifesaver board-clear in late-game as a result. I once chewed through a 36-36 minion a Priest had done you-know-what with thanks to a combination of two Stormwind Champions, a 3-cost minion, and topdecking this for the doggo squad to give me the victory.

Damn shame the devs were savvy enough to not let it synergize completely with Dire Frenzy and become an OP nightmare, but it might still be worth considering doing so regardless for 3 chances to draw four 2/1s and a 5/4, all with Rush. Doggo is fren. Doggo is love.

Love the Zootopia reference

If you craft this with your DK hero power and combine it with pinguine... that would be great value.

2 mana 3/2 Rush + Echo

Charge overrides the rush, and you can hit face with it.

The first thing that popped into my head was fun with Bestial Wrath, but might not be as effective as I'm hoping. But in competitive aspects, not a bad "control" tool and also a nice pick from Deathstalker Rexxar Build-a-Beast.

That's a nice card which is really underestimated, wait for it fellas, it has great potential

 this card is extremely good tbh

Unleash the poor

It's pretty good card for any Hunter deck. Basically, it's 10 damage for 10 mana that is not so bad for just one card.

But what makes this card OP is synnergy with other cards. As mentioned, Scavenging Hyena takes the most benefit. However, there are two more cards that should be mentioned. Essentially, Hunting Mastiff is a one health minion that should (eventually) die.

The first is Cult Master. Hunter has almost no card draw. With Cult Master, you can draw up to five cards (if it survives the previous turn), which is insane or “just” three cards if played on turn 10. These three cards can give you Kill Command or Arcane Shot to finish off the opponent.

The second one is Flesheating Ghoul. If played the turn before and survived, it can finish the opponent. Just use Hunting Mastiff to break a fat Taunt and go face with the 7/3 minion (at best).

For these cases, Hunting Mastiff is much better than Unleash the Hounds. The latter one gives you just one Hound per fat Taunt, which is not so great.

Wow look you were wrong, and this card sucks.  big surprise 

I think people are underestimating the versatility of this card. 

turns put you were incorrect and this card sucks.  thanks for trying

A stronger Unleash the Hounds you play from your hand. seems OK. But everyone knows that face is the place.

I think this card is cute, it's basically just Unleash the Hounds that has more power at the cost of more mana. While that's fun and all, it's not going to see much play because of that.

HOWEVER, assuming that Deathstalker Rexxar get's updated to include this card too, some pretty fun things can happen. Despite anything over 3 mana not being able to be echoed, you still get access to some interesting choices, such as Raptor Hatchling, Ironfur Grizzly, Silverback Patriarch, King Mukla with a couple strong ones sticking out, likeCave Hydra, Crackling Razormaw, Bearshark Ironbeak Owl, Stoneskin Basilisk (alongside it's other three poisonous brethren), and both the crabs. Whether this makes the card strong or not, who knows, Build-A-Beast is situational as hell on what to build, and this card only adds to the possible outcomes.

Overall, this card is not going to see direct play, but maybe it can shine a bit through Deathstalker Rexxar(cuz honestly, double owl or double basilisk is gonna be fun and I want to do that to some poor soul).

I'm pretty sure that Deathstalker Rexxar pulls from the Beast pool. IE; if you play the card in Standard, it will give options from the entire standard pool. In Wild, it will give from every beast in the entire game.

So yeah, could this make Build-a-Beast meta? Probably not. But it will make some awesome highlights.

• The first card pick through the Hero Power will be a card with text. The next card will either have Keywords or be Vanilla.

One thing to consider is that this is a Keyword card, not a text card. So it probably won't work with Basilisk (is his poisonous bretheren), Patriarch, or Ironfur

Another thing to consider is you pick the keyword card (Mastiff) last. So you have to take one of the cheap, typically subpar options (Hatchling, Owl) first and hope they get this card or something good. Also this is gonna be a mostly dead option if you take a 4-5 cost card first,unless you really want the Rush. 

Quote from Sirsir >>

• The first card pick through the Hero Power will be a card with text. The next card will either have Keywords or be Vanilla.

One thing to consider is that this is a Keyword card, not a text card. So it probably won't work with Basilisk (is his poisonous bretheren), Patriarch, or Ironfur

Another thing to consider is you pick the keyword card (Mastiff) last. So you have to take one of the cheap, typically subpar options (Hatchling, Owl) first and hope they get this card or something good. Also this is gonna be a mostly dead option if you take a 4-5 cost card first,unless you really want the Rush. 

Thats actually part of a combo i thought of with it

At 10 Mana

First play Stampede Then Play Timber Wolf Then play Hunting Mastiff 4 times

You just did

12 Damage probably killing most big threats and at the very least 5 cards in hand.

This still feels underwhelming, especially how hard you can low roll with Hunter's beasts.