Don't put your ponies in the washing machine.
Hmmm... oxy will not remove pen, or marker stains. There are special cleaners formulated to remove set in stains. (remove-zit, you can read more about it at
TwinPines - Products, or some people use acne cream with peroxide to slowly fade out stains, or sun light to fade out stains)
Oxy is good for getting some dinginess out of So Soft ponies. You'll need a bucket, fill it with hot water and with the little scoop add oxy until the water is all bubbly/fizzy. I no longer have my container of it, I was sure the proportion of water to oxy was printed on the back. :S
You can leave the SS ponies soaking for a while, but don't leave them overnight or for hours on end. you'd want to avoid giving them tail rust.