Red
In Theros, red is weak, in Journey to Nyx, you have Magma Spray a common that could do the difference. 

The red promo, Spawn of Thraxes, is a playable card, but the throw back of the card is that you spend 7 manas for a 5/5 that kills a small creature or deals a limit amout of damage.

Green 

Theros Green three choises green/white, green/black or green/blue. A lot of players don't see simic like a real deck to play on sealed but the bounce whit big creatures sounds like a great idea. 

The promo, Heroes' Bane, good card, these creature can get realy fast out of control it's a 4/4 that can become bigger for 4 manas.