HITMAN World of Assassination

You can follow the video guide below to complete the mission as Silent Assassin, Suit Only, Sniper Assassin and earn up to 40,000 XP (if you are playing the mission for the first time) to already unlock several starting and smuggling locations, as well as, unlock the following achievement for you:

After that, simply complete the different available mission stories and you should have no problem reaching mastery level 20.