It is shaped like a turtle, with a faucet and a turtle body, and teeth in its mouth. . .
But usually, the tortoise appears with a heavy object, that is, it is carved under the stone tablet, and the tortoise carrying the stone tablet is the tortoise. .
But from your picture, although there are obvious advantages in the mouth, there is no load. .
So it may also be Xuanwu. . .
But normally, Xuanwu is not a dragon head (there are exceptions), but a combination of turtles and snakes with a snake attached to it. . .
Perhaps Xuanwu was carved into this form after artistic processing here. . .
You can judge by its position. .
If it is in the north, near the water, or on the route of the water system of the Forbidden City, it is Xuanwu. .
If placed in front of the main hall, symbolizing good luck, it looks slim. . .
If neither. . . That's an ordinary decoration. . .
From the image alone, it is more likely to be slim than Xuanwu. . .