[@Arcalept]
Okay awesome 
Each witch can only have one familiar since the witch links with them on a soul level. 
The familiar can be any type of animal 
They can heal from extreme wounds but a fatal hit is well....fatal
The creature increases the power of the witch but it is highly risky 
If the animal is hurt the witch gets hurt..capture a familiar and the witch will be unable to leave where ever the creature is captured.
The familiar itself is usually able to speak and some are capable of detecting other witches