Jhin it to win it
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.
Jhin is good both mid and bot, deciding where to play him is up to you. If you go mid both heal and ignite are good choices, botlane take heal. Jhin has a good powerspike level 2 so with ignite you can go for a cheeky first blood.
Jhin loves crit, and IE first gives him tons of power. RFC + 4th shot does insane dmg, Reaver is overall a great item for Jhin. Bloodthirster needs no introductions.
Mercurial Scim gives a bit of extra life steal and most importantly has the QSS effect.
Runaan's gives you enough crit to have 100% and gives some teamfight power too.
Lord Dom's gives armor pen if you need it.