Not bad, but I feel this could've been alot better. This idea had (and still has) alot of potential. I thought the voices were pretty good. Although Butters sounded a little bit too slow IMO.
This can be ignored if the movie was actually funny. And although some parts made me grin, it kind of felt like you rushed the script or something, because if you worked out those jokes and for instance Cartman really be the toxic shit he would be in league this would already be alot better. As this was targeted towards the LoL audience, what Cartman just said is nothing compared to what they are used to on daily basis.
I loved the stupidity of Butters in this movie and it was really the best part of it all for me, but that could've been better as well. I hope you'll keep improving and I'd love to see what future movies you'll submit to the NG portal, I'll be following your progress. :)
Also don't mind fanboys like that \/
the fact you're showing your work to the world is admirable.