After some tweaking and sourcing, I've made some alterations to the list to refine archetypes and reduce the mana curve, as well as to rebalance the representation of 'colours' to be more even.

Of note, this update brings in Walking Ballista, which can infinite combo with Heliod, Sun-Crowned or Cleric Class + a source of lifelink. While in general I've tried to avoid 2-card infinite combos, I believe both cards will be highly prioritised in the draft so that the chances of one person getting both is fairly low - while being a 9 mana combo to do all on one turn allowing interaction to still occur.

Changelist

• ❌ Sunscape Battlemage
• ❌ Heliod's Pilgrim
  • Redundant to Invasion of Theros
• ❌ Mesa Enchantress
• ❌ Angel of Jubilation
• ❌ Felidar Guardian
  • Replaced by ➕ Emiel the Blessed. While Emiel is slower, the ability to repeatedly blink and put +1/+1 counters makes it a powerful and desirable card.
• ❌ Platoon Dispenser
  • Replaced by ➕ Maskwood Nexus. Helps reduce powerlevel of the midgame, and Maskwood Nexus enables tribal corner cases.
• ❌ Regal Caracal
• ❌ Evangel of Heliod
  • Redundant to Reverant Hoplite
• ❌ Disenchant
  • Removed as many hybrid cards do the same thing, and I want to encourage people using them instead.
• ❌ Divine Gambit
  • Replaced by ➕ Gideon's Triumph, which can slay the dragon.
• ❌ End Hostilities
  • Replaced by ➕ Mythos of Snapdex, as both can fill the role of dealing with the equipment deck/being a sweeper, while also requiring Mardu mana to be optimal - desirable for the theme of the cube.
• ❌ Portable Hole
  • Replaced by ➕ Baffling End, which can permanently exile a problematic creature while also making green tokens.
• ❌ Mysterious Limousine
  • Replaced by ➕ Golden Argosy, which lowers the curve and better serves the role of upgrading prototypes and flickering creatures.
• ❌ Pacifism
  • Replaced by ➕ Planar Disruption, a strict upgrade.
• ❌ Banishing Light
  • Replaced by ➕ Leyline Binding, because it's funny.
• ❌ Omen of the Sun
  • Replaced by ➕ Summon the School, which while slower and more expensive, has recursion with tribal interactions.
• ❌ Starfield of Nyx
  • Replaced by ➕ Hallowed Haunting, mostly to prevent Enchanted Evening destroying all your lands.
• ❌ Vexing Scuttler
  • Replaced by ➕ Distended Mindbender to balance the colour representation.
• ❌ Shalai's Acolyte
• ❌ Loyal Cathar
  • Replaced by ➕ Panicked Bystander, which performs better in the mid game and synergises with lifegain.
• ❌ Cleaving Skyrider
• ❌ Rally the Peasants
• ❌ Hangarback Walker
  • Replaced by ➕ Walking Ballista, which can slay the dragon.
• ❌ Witch's Oven
  • Replaced by ➕ Springleaf Drum, to both enable 'when becomes tapped or untapped' effects and to ramp.
• ❌ Thran Power Suit
  • Replaced by ➕ Nettlecyst, which as a living weapon is a black creature, which is better colour distribution.
• ➕ Batterskull
• ➕ Discerning Financier
• ➕ Late to Dinner
• ➕ Stonecoil Serpent
• ➕ Pollen-Shield Hare
• ➕ Azorius Herald
• ➕ Mirror-Sigil Sergeant
• ➕ Shrieking Grotesque
• ➕ Stonybrook Schoolmaster
• ➕ Champion of the Parish