I didn't know a thing about efficient deck-building, tournaments and the like, so it couldn't have been that
There's no other card that gives you two mana for one with no downside, and this ultra-consistent ramp card can go in any EDH deck, making it an auto-include for most people who aren't making a conscious effort to be hipster
: Put a +1/+1 counter on this creature, then you may reselect which player this creature is attacking
Sword of Truth and Justice works particularly well here because it gives you +1/+1 counters and Proliferates
Playing this on turn 2, two or three turns before the commander hits play, ought to be enough to reach six humans for owyns main trigger
Nightmare is a powerful mono-black payoff thats too slow for most Magic formats these days, but it still boasts an impressive body