PARIVISION support Edgar "9Class" Naltakyan explained how to play Marci in patch 7.39c for Dota 2. He suggested an optimal build for the heroine and gave a brief advice about the general strategy. The mini-guide was released on the team Telegram channel.
You must aim to win the lane with Marci, then help the mid with runes (since she can save with the facet and attack). After BKB, you already have a lot of physical damage, so you can go forward and fight on your own.
Marci was significantly buffed in patch 7.39. She got an increased agility gain and improvements for Dispose and Rebound. The following letter updates (a-c) didn't change the hero.