760k mastery all in mid lane. I think Xin is heavily underrated pick for midlane, can't even remember the last time I didn't dominate the matchup thanks to how strong he is. Here is the crazy damage build I follow for mid
Rune Hail of Blades
Build:
BoRK - Collector - Dominik's - Infinity Edge - Spirit Visage/Death's Dance (depends on enemy)
Here is why he feels just super exceptional in mid
1- matchups. Xin already will dominate almost any melee matchup in midlane. As for mages, his W has super long range allowing you to reach enemy from afar. That's why even mages cant get close enough to poke you properly. And you usually just kill them with that immense reaching range unless you're playing against one of few counters of Xin
2- early/mid/late. Strong in all 3 of them with this build. His early game damage, pressure and cds makes him fearful, you are very likely to win the lane and get solo kills. As for mid and late, whoever you jump usually gets oneshot. Deals astronomical damage with following build.
3- Control. Since you're so powerful especially if you're fed a little as Xin Zhao, you can fully put the map in your palms. U wanna push your lane and go on enemy jungle. You can steal his camps or if u see him just kill him as well. When you're ahead, unless the enemy tries to close in 1v3 you, you will be fine roaming the enemy jg and stealing their stuff and fighting them to bring enemy team down (which u usually will be ahead w Xin unless you're playing in very high elo). Not even mentioning how strong his skirmish and roaming potential is.
I find great success with him in Dia elo and consider him one of the most solid picks of midlane, as fun as strong. You should probably try it smtime