Replacing some underwhelming white cards with similar cards that are just more fun.

Just replacing some underwhelming red cards.

The mana investment for Short Sword was worth the reward. Diamond Mare is a great replacement for the same investment.

Blessed Respite is just better Root Snare that also combats mill. Squirrel Sanctuary is a recursive creature that's cheaper than Dripping-Tongue Zubera. Tower Defense is another instance of reach to combat the additional flyer in Black.

I like Callous Dismal and think this is a great format for it. It replaces Bind the Monster because even though it's 1 cmc, it doesn't answer a turn on threat any way. Opt is kind of just a tempo loss when playing with such a small library, so Rookie Mistake comes in as actual turn 1 interaction. Towering-Wave Mystic is the second mill support card in the list. I don't think I'll be adding any more, but Wishful Merfolk was just a placeholder.

Looking at some other lists I saw black doesn't need quite as many creatures so I added some more 1 mana interaction. I also added some late game closers like Poisonbelly Ogre and Returned Reveler to give mill a little bit of support.