At lvl 3 you will unlock your second Mastery. This skill is required to unlock ANY tier 1 skill from ANY Mastery. Put 2 points in the Mastery bar, which will unlock the skill 'Multi-Master Level1'.
After you enter the mod and reach level 2, in the Mastery selection screen choose Rune Mastery. Launch the game and load the mod from Custom Quest menu. Place folder 'Multimaster' in 'My Documents/My Games/Titan Quest - Immortal Throne/CustomMaps' as you do with any non-Steam mod.
This mod allows you to learn any skill from any Mastery without cheating.
