4 ideas

[Thalas]

Small Dragon
Damage: 1 Hp: 3 Cost: 4  (upped Damage: 2)
Fire Breath - Attack the targeted monster.

Ground Cerberus
Damage: 2 Hp: 2 Cost: 4  (upped Hp: 5)
Eruption    - Every monster have 50% chance that it will be damaged by 1. 40% chance of destroying opponent's pillar/tower. 

Medusa
Damage: 2 Hp: 3 Cost: 5  (upped 4  )
Turn into stone - when opponent uses 3 spells, you can turn creature into Stone Statue

Stone Statue
Damage:0 Hp: 1

Ghost
Damage: 1 Hp: 2 Cost: 1 
Possesion: destroy this card,  gain control of targeted monster to the beginning of your next turn

EDIT: Extended effect of possesion

[ajm6]

Small Dragon- I like this one the price isn't too high so its not too powerful, only thing that might need to be changed is the ability price, but that's just balancing.

Ground Cerberus-I like the monster part of eruption, I don't like the idea of it also attacking the pillars. Other than that I,like the idea.

Medusa- Great idea, but I'm not sure the ability can be triggered like you have it. Perhaps just give it a normal cost.

Ghost-I'm not sure about this one. I just don't see myself using it.

overall good ideas