Not Updated For Current Season
The masteries shown here are not yet updated for the current season, the guide author needs to set up the new masteries. As such, they will be different than the masteries you see in-game.
Corki is a strong First blooder if you're using this build. You might want to switch the Phosphorus Bomb with valkyria if they have strong ranged players so that you can catch up with them because you are able to kill most champions in like 3-4 shots.
Corki can be alone at the upper lane but i prefer not meeting kassadin. Because he can avoid corkis ultimate with hes ulti ''teleport'' + the kassadin ulti lets him to get away easly when you start the gattling gun which is your biggest damage source.
Dont be affraid of picking up 1v1 fights when you're the same level and with the same amounts of items.
Corki can run into the enemys first in teamfights because when they target you and got corki down to 50% hp they perhaps will start chasing you when you turn around. Thats when you slow them with frozen mallet and kite them while your teamates bring them down. Turn arround and shoot sometimes to keep the slow active and also fire ultimates. When they get close or slow you, just valkyria away (or exhaust) if your're in panic.
If you're running low on hp !!! DONT RECALL !!! stay away with a good distance using ultimates that will provide with alot of help to your teamates if they are in trouble at example 2vs3.