Omni is my ultimate go-to hero for winning pubs; his job is quite simply to keep people alive. The reason omni isn't picked in competitive dota is that he has a great number of weaknesses. He is mana starved though most games, has low cast range/long cast time, offers almost nothing in the laning phase and his ult and repel can be removed with a purge. This guide will help you hopefully understand his strengths and weaknesses better and help you to push his strengths and combat his weaknesses.