With Combi you can unlock a Set called Master Set.
It exists for Male and Female. You completly unlocked it, if you reach Master-Level 36 but thats a long way. If you have a combi with an Player, you will get 1 Combi Exp for each level the Player goes up ( until level 13 ).
I'll put it in simple steps for u to understand it more properly,first u must make a combi (u can do this by pressing right click on ur friend in game )... that's it now u have a combi as .Aziel said above u can unlock special dress also called *master*...the more ur partner increases his level or ur level increases the exp of the combi also increases. Combi can also increase by playing together.^^
)... that's it now u have a combi as .Aziel said above u can unlock special dress also called *master*...the more ur partner increases his level or ur level increases the exp of the combi also increases. Combi can also increase by playing together.^^ 
^^
