You should play a mission with a good amount of enemies to use your wingmen against. You need to use them 20 times throughout one single mission. This is not accumulative within separate missions. To gain prowess to use the wingmen, defeat enemies, collect coins, and successfully counter attacks. With the Burning Spirit Battleset equipped you should gain this really fast. Just use the Battleset on the following level after you gain and equip it. Get the bar full to all three yellow bars with the icons green instead of red. Press the three times while targeting an enemy. This will count all uses and does not have to be on separate enemies. If you fail a mission and have to use a life, the amount of times the wingmen used will carry over to the next life, even if dealing with the same enemies.