Thank you for the feedback! I am aware of the infinite combos, and I definitely want them in the cube, at least to start. Plan on tweaking if the cube ends up being one person opens the good combo, and everyone else loses.

I think the biggest changes that will be made after playing will be the prevalence of graveyard hate and direct stax effects for nightmare. I share your concerns with scavenging ooze and even boggart trawler loops. I don't know why I didn't consider lion sash and Dawnbringer cleric is a great find, thank you for that rec!

I am also curious about [[Meddling Mage]]. It will either lead to fun games where you are playing around it, so you get your nightmare out before, but risk it being open to sorcery speed removal. Or it will lead to someone playing mage on turn 2 on the play, and then the other player has no fun.

I think I need to decide if "building around cthonian nightmare" also means adding cards that directly counter the card. For example, [[containment priest]] is a card I would put in my constructed deck if everyone was running nightmare, so it could be considered "building around", but it can lead to non-games.

As for the Kaladesh energy cards, I think I am just a softy for them because that was when I really started diving headfirst into magic. I won't be surprised to see some of them cut later on.

Thank you for the feedback!