This is an ally that needs a little more building around than the others in Cable's precon, but the upside is tremendous. Even without a minion in play, dealing 2 to the villain on entry makes up for only having 2 hp, putting this on-rate with other 3-cost allies, and when built around you should have no problem getting 3 damage. With one minion in play, Sunspot becomes a Valkyrie, and with two minions engaged with the same player, Sunspot can do 11 damage in one turn and be ready to block immediately in the villain phase...simply insane. If you want to play a -theme deck, be sure to include Captain Marvel as well. I look forward to playing an Iron Man deck with Sunspot, since his Repulsor Blast also encourages building with energy resources. Thor is another good choice, who makes lots of with God of Thunder and uses it to power Lightning Strike.
Do note that while you can always overpay for cards in Champions, you can't count them towards an ability like Sunspot's above the card's printed cost. See hallofheroeslcg.com for the relevant ruling on Moon Girl, which uses the same language as Sunspot.