The God side, a mono Green creature, effectively gives all of your legendary creatures the ability to generate mana of any colour
It can be hard to hold up four mana, but if you sacrifice a large amount of creatures in one go, you can instantly replenish your board
However, the disadvantage you're creating for yourself is almost always less than the total amount of disadvantage you're causing to your opponents , especially in black where you have ample graveyard recursion at your disposal
With Green, you have a handful of fighting creatures like Wicked Wolf, Thorn Mammoth, and Kogla, the Titan Ape, but they're fairly scarce on their own
Thats the best of both worlds when it comes to build-around cards