Naix in a nutshell
You are a strong jungle hero from feast. Remember to assist your lane with ganks with your powerful slow. Due to naix's lifestealing and ult giving tons of health armlet is an amazing item for him. Extend this out into a desolator and knock people's teeth out. If you feel comfortable getting a midas in under 10 minutes go for it, it is a very strong item for naix and the attack speed has good synergy with feast.
I've had great results from Mjollnir but I consider judging when it is a good decision is too situational to be in the simple guide.