Ah, so it's this event again. A similar one was running when I started playing. Fun, but being limited to the recharge on your attack points is annoying. As is winning stupid cards like a 1-star Sarina and having them only be able to be claimed by a verified account (wat).
Oh well.
Also, what does the little option do when you get a rival challenge that costs the small amount of stamina?
EDIT: I still don't know what it does, but it lists all my production members after I hit it.