Due to the format restriction of running only CMC <3 cards, certain cards whose effects are conditional on targeting cards with mana value 3 or less, or even mana value 2 or less, become much more powerful and competitively costed, such as Dread Fugue, Change the Equation, Claim the Firstborn, or Portable Hole; Dark Confidant will only ever bonk you for a maximum of two life, ensuring plenty of low-cost extra card draw as long as it sticks around.

!!The rest of the description is under construction!!

The heart of the cube.
The exception to this rule is Scourge of Nel Toth, which gains "This card may not be cast by paying its mana cost." Initially, I put a blank sticker its mana cost, only to realize that a player would be able to Unearth or Recommission it as its mana value was now 0, and so I peeled it off again before someone could go and try that. Force of Will was previously in the cube with this same stipulation, however a player pointed out that when another blue card is not in hand and it is not castable for its mana cost, it becomes an entirely dead card, and so back in the binder it went.