Okay, so this is basically a sub specie of Snakes, limited to certain people who have the Snake contract. This new species, which had evolved over time, adapted to harsh conditions and as such, made them more deadly in terms of sensing, the amount of damage they can withstand as well as having gained a passive ability of camouflaging with the surroundings to escape predators and foes alike. So in short, they are basically more advanced and more dangerous, than a normal snake. And through using this technique, one is able to summon the Crotalinae Specie, instead of the normal snakes, allowing them better perks in battle. Pretty damn useful and lovely. Great job with this technique.