Defeat Boss Lenenov, Boss Belikov, Boss Osipov and Boss Bassinov within 10 days. You need to be level 20 or higher to do the boss challenge. For defeating these Bosses you get an item and a Mastery Item for defeating all four of them. The stats of these items increase each mastery level. An attack at bronze mastery is File:Stamina icon.png 1 or File:Stamina icon.png 5 stamina each. You receive File:Icon experience 16x16.png 2 or File:Icon experience 16x16.png 10 Experience.