Not too long ago I had to deal with such a situation. Land lord wanted me to pay the whole lease( 1 yr. ) to move out. But I pulled the lease out and he had to back down. He had my starting date wrong and I still was able to give him the notice required.
But one thing I learned is renter's have the rentee's by the ... (well you know.) That's right by the wallet. These lease's are drawn up to pretty much say they can do whatever and you have to follow the rules they have and that's pretty much that's the way it is. And if you want out early, YOU PAY
With the cost of lawyers I don't know about a lawyer but you can maybe look up the rules of your state. But most lease's are drawn up to follow them because most the time laws go in favor of lessor's.
If you didn't move out and they give you notice because you didn't get rid of your snakes, will you still have to pay the fine of 750 ? And how many days will you have to be out? These things depend on the state I figure.
They might just not like you having snakes, some people hate snakes and knowing they are in the building makes them nervous. They might have had complaints about it. Don't know. If snakes violated the agreement I figure they would tell you that. But instead use the mold excuse.

Here's the big question? Is selling your snakes an option? Maybe some with temporary homes. That way you can make some money save having to pay 750 and then when things change down the road get some more snakes or (some back.) Some people on here ( breeders sell snake's all the time ) would you be willing to do that, the other way will cost you quite a bit of money and then give you a bad reference as well. Just saying something to consider.