The Katarina build for Mid is Hextech Rocketbelt and Electrocute. This LoL Katarina guide for Mid at Platinum+ on 13.23 includes runes, items, skill order, and counters.
Katarina Counters
50.6%
(+0.3%)
43.6%
(+0.7%)
6.1%
(-0.1%)
6.4%
(-1.5%)
859
(-26)