Will it damage the battery if I use my MacBook Pro while playing WOW or just using it, while charging?
If your computer says it's charging but the battery level percentage is still going down, then you're putting way too much stress on it. It's a rare occasion, but I have seen it happen once or twice.

If your battery percentage goes up, no matter how slowly, you should still be okay to use it while charging.

EDIT: Sorry, I don't know whether or not a charging-but-decreasing battery is actually bad for the hardware. I was just thinking that it's a situation that you should know could happen if you're doing a lot of battery-intensive processes. I don't know whether or not it damages your battery in the long run, just that it's possible that plugging your charger in won't actually charge the battery as quickly as you're draining it.