I recently purchased my very first DIY Kidrobot vinyl toy. I bought the Trikky toy, which is a cat in a blank white slate. I made the mistake of using washable markers the first time I tried to decorate it. Luckily, they truly were washable and just came right off with water.
My second mistake was using Sharpie pen for his nose and mouth and then later deciding to make it bigger.
So I tried again with basic craft store acrylic paint and cheap brushes. I did several thin layers to build up the colors and finished it off with hard coat Mod Podge to seal it.
I think it turned out pretty great for my first try. Although, I'm not happy you can sorta see the Sharpie under some of the paint. But I've already bought my second Trikky to try another custom paint job!
Have you tried one of these DIY toys? They have them in smaller sizes for under $5 bucks if you want to practice a lot first ;)
P.s. I gave my Grumpy Cat toy to my friend/co-worker and she loves it!