Mejeiwan is strong but I'm stuck

Metal bird? I thought I could use defense penetration for this! But it unexpectedly targets the enemy with the highest HP, what the heck are you guys... I could advance by using multi-hit attacks like Mejegunman, but looking at the clear formations for the fast bird, it seems I need to learn freeze, and I don't think I can make it in time for the hidden quest~ The game itself is quite addictive, so maybe I should have just done the time quests for other offers with 60-day periods and downloaded from elsewhere? But since there was a dungeon this time, dungeon判定 might require going through Playio, and if you don't get lucky and pull strong units, the hidden quest is impossible with such a short period, this is a無理ゲー.