Talk:Black Panther (disambiguation)/@comment-68.190.25.248-20130131221808/@comment-70.118.6.70-20130201043954

Yes, you need to max both cards before fusing to get the double bonus (10% vs. 5%). You then max the fused card..aka M/M.

From the fusion page:  "In order to maximize card strength, a card should be boosted to its maximum level and fully mastered before fusing it to the next rarity. Cards that are fused at maximum level provide 10% of their current stats to the final card instead of the usual 5%. While maximizing mastery provides a direct boost to the cards, during fusion it also contributes a boost to the mastery of the final card equal to its current level."