This card lets you choose a number because it changes what the effect is
The mechanic backup shines here as a way to pump creatures and add abilities to them, and rares like Boon-Bringer Valkyrie and Silverback Elder are game-winning bombs
While definitely a flavor win, accurately selling the existential threat the Eldrazi posed, flavor cant ovveride fun
On its own merits, this would already be insanely good, as enabling a Mana Crypt that taps for 3 colorless mana, a Basalt Monolith that can go infinite with Kinnan on turn 3, or a Birds of Paradise that taps for 2 mana of any color is ridiculous value
It's also an answer to [Screaming Nemesis], which ruins the lifelink of Atraxa or Valgavoth, so mono-red might be stopped just by playing this card