Basically, you're kind of selling the drawing to them.
Of course, you have the rights to use it for whatever you want, but you can't sell the drawing to anyone else not listed in the contract (basically, only they get to use it for profit-purposes).
You're not liable for any copyright infringements that might get run across with Hasbro or anything, because it's fanart and not official art. If you want, just contact them and ask them if they'd be interested in using your art (you get to choose which pieces they can use, and it can't be OC work, apparently. Has to be cannon) and if you could see a copy of the contract for yourself to review. You don't need to make any decisions soon, but it'll not only allow you to print your work for different merchandise (shirts, buttons, mouse pads, stickers, etc.) but you can also make a little extra money on the side~ c:
That sounds really cool! And I need some money on the side. Well, I need money, period. ; ; Do you know what's the percentage of the income you get from each drawing? Cause right now, I'm almost done with all my commissions, so my plan for now is to draw a few canon works just to come up with a few ideas, then contacting them and show them some examples.
Plus, if that doesn't work, a friend of mine showed me a website where you can make your own shirts and sell them yourself. Personally, I have no idea how to do that, all I know is that that's how Slug does it, but that website seems to make things a lot easier.