House-Keeping:
Not much to be said here, mostly just adding cards that encourage more aggressive gameplay or support archetypes in a manner I prefer.

Justification:
Song of Freyalise, Obsessive Skinner, Elite Scaleguard, Hagra Constrictor: Support the +1/+1 counters archetype.

• Obsessive Skinner is more niche than Werebear but I like Reclusive Taxidermist more and don't feel the need for repetition of the effect.
• I don't like Basri's Acolyte. Lifelink can be oppressive against aggro decks and I think the card is just kinda ugly compared to Relief Captain. Not much other justification here.
• Hagra Constrictor is just okay as a 2/2 menace for 3, but I like that it encourages a strategy otherwise outside of Black and has some incidental value with Bloodsky Berserker, Electrostatic Infantry, and other aggressive cards.

Unholy Heat, Heartless Act: After my "All Removal Comes with a Price" update, I wanted to find removal that would deal with large threats without feeling unearned. Unholy Heat offers even more reach than Flame Slash did, but I like that it feels more earned than the unconditional 4 damage did. Heartless Act is an unconditional removal spell in a lot of environments, but in the context of this proliferate & counters heavy cube, I think it punishes more of the "cheat" threats like Tolarian Terror without punishing the high-investment counters archetype. Interested to see it in action.

Frenzied Saddlebrute, Thrill of Possibility, Deceiver Exarch: These cards offer effects that are quite common to their respective colours and underrepresented in the current design.

Alirios, Enraptured replaces Mirror Image. As much as I would like to keep a clone effect in the cube, I find there aren't enough large creatures that you'd want to copy, and playing it on curve is just not effective. Alirios, on the other hand, is just a very efficient two-creature body with some caveats. Pretty happy to play this in most Blue decks.

Akoum Hellhound replaces Flametongue Yearling to encourage aggressive decks and support the emerging landfall-aggro pocket archetype. Great synergy with the bouncelands and Evolving Wilds, less mana-intensive.

Davriel, Rogue Shadowmage gives Black its first monocolour planeswalker and replaces the only card with the foretell mechanic.

Future Considerations:
If more foretell cards are printed, I'd be happy to add Vengeful Reaper and a selection of other cards back to the cube. I think the mechanic does a great job of encouraging splashier decks, but I don't like it without more uncertainty as to what the card being played is.