Scooby Doo: Sitting Scooby Scared Figure (Character Options, 2000s)

Now here's a weird figure, that we don't quite understand. 
It can sit up right, and is the size of a standard Scoob figure, but it has this little weird circular thing on it's leg, that we don't get.
Is it maybe to put him on a pen? Was it a part of a bigger figure set? 

We've been scouring the internet to no avail, but it seems to be quite hard to find at least. 

Condtion: Great