Mai 40 is easy as hell to farm with unhappy girl, basically any character with the skill "alpha" can farm Mai for 7-8K consistently. See my suggested deck in the comment section of "How to beat/farm Mai Valentine Lvl 40"
No Union Attack in the shop. Non-event Gate LD SRs only. As for the rest of this thread, if you're having a hard time getting an Econ, you should definitely get it. By far the best and most splashable card in the entire game