The past couple EVO tournaments for Street Fighter (which is, for people who don't follow the FGC, the largest tournament in the US for fighting games) have been won by some pretty unexpected characters, which I like; nobody really considered Gen to be a powerhouse until Xian pulled it out, and I'm pretty sure Rose was thought to be solidly low tier until Louffy demonstrated that she could make really effective use of her normals (and also lucked into some people who didn't understand the Rose matchup and e.g. kept on spamming Sagat's fireballs when that's a pretty terrible thing to do against Rose).

I feel like there are a lot of characters in SF who are pretty viable, and some of them just require a lot more work than others. It's pretty well understood how to play a shoto like Ryu or Ken, but the downside is that when you pick them, everybody knows what to expect from you. If you can put some solid work into a low tier character, you can often pull off some really unexpected stuff and occasionally shift the tier lists.

Another good example of this was Canada Cup 2013, 5v5; NE Asia's Dakou picked Dee Jay (a decidedly low tier version of Guile) and ended up destroying a bunch of people who really expected to win. The commentary on this set is a lot of fun just because you can tell the announcers are so surprised: https://www.youtube.com/watch?v=rcMwzw6EbMg