I have about 17000 credits now, but I want to reach about 30,000 before all the cool Halloween stuff comes out.
So far, the best way for me to get credits, is to play fireworks. I get about 1,300 per game, that is, if I don't get first. I think that is totally ridiculous. Good thing is, though, if you keep coming in second with 240,000, you get fireworks magic every so often. So on top of a bunch of credits, I am getting magic too! WOOT
Just something to add:
I was looking at the list of items being sold, and I was figuring about 2,000 credits per costume, and about 500 credits for a piece of clothing, and it came out to be around 25,000 credits!!! (not to mention all the halloween stuff that will be coming out!)