Hearthpwn

For some reason, neither the pandas nor the worgens are beasts. 

They are sentinent

That is insanely broken.  Consider a card like Lowly Squire for example.  It even has an activation requirement.  Sure it starts with slightly better stats but it is outscaled in a single turn.

Adapt, taunts, + health effects (coin power word shield?), and others become problematic.  Forces the opponent to answer immediately - not something you usually see out of a 1 drop.

The question is then, what would make this idea of a card balanced?

Would this card be balanced if it only started with 1 health?
What if it only gained +1/+1?

Are either of these balanced?

why aren't Pandas and Worgens beasts?

Because you haven't been sharing whatever you are high on with everyone else.

Quote from Crusader2010 >>

I'd make it gain attack at the start of your turns and health at the start of every 2 turns. The wording is going to be hard to do right though. It's not like mana wyrm and the trogg didn't require immediate answers. That's the design direction for this game - make op card that force the meta in certain directions, usually per class. That's how they control the rock/paper/scissors implementation.

Your panda card is definitely not op, especially with a +1/+1 gain. The trogg could get +4 attack in like 2 turns. Nothing different. And, when designing a card, you should not care about the fact that it can be power word shielded. If that was the case, even Deathwing is op for 10 mana. In a worst case scenario you can restrict the card to a certain class. The panda is not worse than having Patches and a 1/2 on board on turn 1. 

Shitty design decisions for the game (aggro ftw) require op cards to make kids play and to get others fed up and leave.

Quote from TheKaldorei1 >>

They are sentinent

They aren't considered beast because they are considered humanoid in the game of wow which what hearthstone is based off of if you didn't know