Why Corki mid is suddenly so popular
If you've watched any of the bigger League of Legends streamers in the past couple of weeks, or you've caught a recent game of the NA LCS, you've seen a ton of Corki. He's even being played in lower elos, and sure the results aren't as great there, but his playrate is still spiking.
So, what happened? Corki wasn't popular this time last month, and he hasn't had any big buffs or item changes, so it's sort of baffling that he'd become this popular so quickly.
In fact, he went from being played in less than 0.5 percent of games in the mid lane in Patch 7.11 to being the sixth most played champion in the lane only two patches later, according to League stats site Champion.gg. This sudden spike in popularity came from one very tiny change that ended up making him much more viable in the mid lane. In Patch 7.12, he received some smaller buffs to his base attack speed and attack damage, but the biggest change was to his passive. This converted half of his auto attack damage to magic damage instead of physical, and it was shifted to be 80 percent magic damage and 20 percent physical.
This means that Corki builds a ton of magic damage with his auto attacks the more he builds AD, which is a little confusing, but it allows him to build more magic penetration, because it will now affect both his abilities and his auto attacks. More importantly, though, is that his early-game damage is much more effective. This is because most players run flat armor runes in their rune pages, but scaling magic resist or no magic resist at all, opening them up for more magic damage in the early stages of the game.
Combine that tweak with Corki's phenomenal wave clear and mobility, and you have a new, excellent option in the mid lane. He isn't the first marksman to make his way to mid, however. Lucian has been running amok in the mid lane in both solo queue and pro matches lately as well, but for different reasons. Mostly, it's because he's OP, but it's also because he can deal very quick, consistent damage in a pinch to punish mid laners with cooldown windows, like Kassadin and Orianna.
If you're getting annoyed with all of the Corkis, you better get used to it for now, because it doesn't look like he's going anywhere anytime soon.