Worthy Knight looks like a respectable payoff for Knight tribal. Comparable to
Hero of Precinct One, although obviously different requirements.
Claim the Firstborn is adorable. I'm a big fan of miniature versions of cards (
Unearth,
Natural State,
Spell Snare, etc). Is the cheapest
Threaten effect available? They almost never see constructed play, but at 1 mana, it has some potential. I'd love to see
Claim the Firstborn +
Spark Harvest (or some other sac outlet) in constructed.
Syr Carah, the Bold is intriguing. Burn-based storm? A bit too linear for my taste in EDH, but could make a viable burn deck, ignoring the whole 'five mana commander with no immediate impact' thing.