Masked Man is a great support that changes the way you play the game. His mystery truly works wonders. The ability to (more or less) take the enemies position 1 ninja out of the equation in round 2 will help you especially against people that have more initiative than you. However Masked Man is a support that is unable to win matches for you without a strong position one. But once you obtained a strong position one he is probably the most important ninja to get.

Since you do not own any typical position one ninja (i am thinking about Shisui, both versions of Minato or Deidra Edo Tensei) i would recommend you get one of those. Obtaining Shisui is probably the best choice. That's if you can redeem him in the lucky board. This would get you lots of power and a good ninja. Masked Man (or Jonin Minato) can be obtained by collecting their fragments for free during Fateful Choice or Mission General Mobilization. It would take about 6 Months to collect the frags for one of them. I would advise you against obtaining Jonin Minato (Initiative), Edo Tobirama (Summons) and Earth Grudge Kakuzu (Ninja) since they require certain things that F2P players normally not have.