This battle will likely take level 40+ normal silver cards at minimum, unless you have good gear. It would be very difficult for normal cards to win the last few matches, however.
Match 3 Edit
Challenge: Regeneration! (~0.8% maximum health restored for the whole enemy team per second)
Challenge: Radiation! (You lost ~0.8% health every second)
Challenge: Countdown! (You only have 2 minutes to defeat your opponents)
This match awards 3 energy cards.