I think your snakes need little more variance.
For example.
Gravity- Bind. Target creature can't take action until snake is destroyed.
Earth- Burrow. Chance to hit 4x damage when burrow.
Dark- Bite. Infect the target creature.
Death - Deadly Bite. Infect the target creature for 1-2 poison counters.
They all follow possible themes for a snake, and they give more diversity. Take and leave whatever you want from this. I just think it would be more interesting.