I know a ton of stuff about snakes personally and in the NV. The main reason I wanted to pick them up is because they are way more developed. Especially more than slugs, which is what I previously had and I actually like snakes. Since there are only three sage modes, Toad, Snake and Wood, I figured I would pick up one of the two animal contracts that would grant me access to an SM one day, being that I will never master Hashirama for wood SM even though I love the wood element. Also, I originally wanted to sign snakes or salamanders anyway so I mean, hey. Might as well try something new.
Anyway, snakes in the NV reside in the Ryuchi cave, varying in size but mostly summoned on a larger scale in battle. My favorite snakes being Manda and Manda II due to their threatening size and looks. The signers of this contract that I know of, or at least relevant characters would be Orochimaru, who is a master of this summon, Sasuke, Kabuto and Anko. I think that is it. I may be wrong as one could have slipped my mind, but I think that's it. When it comes to their size, you can compare Manda or Manda II to Anko's snakes that come out of her sleeves or Orochimaru, as he does the same. While Manda on the other hand, wouldn't be able to fit in anyone's sleeve if you wanted him to. If I recall correctly, it was Manda II that "strangled" the Island Turtle. Their hunting abilities are amazing, as they can sense heat or smell their prey, leading their summoner to whoever they are after. There are plenty of snake variations/bosses/whatever you would like to call them. I have mentioned Manda, there is also Aoda, the one in my sig, etc, there were plenty of other unknown/unnamed snakes summoned in the series as well, that looked just as cool and threatening as the main ones. I also believe snakes can also hide certain things in their bodies by digesting them and then regurgitating them.
They're all around cool, very useful in battle in the RP, and also, they are cool. Times 2. Probably my favorite summon in the series in front of salamanders and slugs. I feel like I will make a great connection with this contract.