Gideon planeswalker -- wow, they're still steadily churning out variants on "become a creature" ability, I'm still amazed they managed more than one!

Spell mastery -- it vaguely reminds me of other "combo lots of instants and sorceries" mechanics, except it's balanced to aim at a number of instants and sorceries it's possible to actually play in a plausible deck (rather than mechanics that eg need N copies of inst/sorc with that mechanic).

I love the new Gideon. He's reminiscent of my Ara, Hope Unfound, only better.