I mean, it is know to be associated with dark wizards. JK, you are just setting up slytherins for failure. Why cant it be something like a golden eagle? that fits it so much better. (Suggestion for mascot by @Queenquill ) fox is another candidate (by @UnicornSaysHi )
"Golden eagles are surprisingly sneaky, they fly low to the ground when hunting so their prey doesn't know they're in danger until the golden eagle has already caught them, and golden eagles are really smart too. I personally think golden eagles fit Slytherin better than a snake actually, can you imagine the Chamber of Secrets monster if the Slytherin animal was a golden eagle?" - Queenquill