The wording on Mage Ring Responder is a little unclear. I've been playing puzzle quest games for a while, so I understood it to mean you have to match 5 gems of one color, which has had special effects in other PQ incarnations.
To answer your question, it would probably be overly strong if you could just make two 3-way matches at once to activate him. If you can give him Vigilance, he makes a nice blocker!
Wow, even more.Show Creature Types
There is at least one creature (Shaman of the Pack) which cares about creature types but no creature types are shown on cards.