Sunfire is the 'Villain Boost Assassin'. Unfortunately, I feel like he got shortchanged by being a 'after you play' ally.
Since the rest of his stats are so average to meaningless, his special ability is the only reason to include him.
And while that special ability is amazing, it only triggers when he is put into play. Which means he is most valuable as a potential card, which is a horrible trait in Champions, as holding cards reduces your effectiveness.