Borborygmos ' Beatings (Rav 2.0)

[asi]

Borborygmos ' Beatings
Enchantment- [subtype]
At the beginning of your combat step, you may reveal the top 4 cards of your library. If you do, put any creature cards revealed this way into your graveyard. Creatures you control get +X/+X until end of turn, where X is equal to the number of creature cards revealed this way.

The problem here is obvious: it is a red card, but it should feel red/green and fit to the gruul. I thought about adding "trample" somewhere, but it would remove the "Song of Blood"-feeling, I think. So, any ideas how to solve this problems?

[jeek]

The easiest way to make it green would be to change the ability to +X/+X

[asi]

But how much mana should such a card cost? I'm thinking 2GR, but I'm not sure. Good idea by the way.