At three, you get your manas worth and huge card advantage, which should be enough to close out the game
Bringing the nonfoil value of this Secret Lair to a staggering $53.50 without factoring in any Universes Beyond premiums, grabbing this Secret Lair for its $29.99 price is a no-brainer
Cards with ferocious like Shamanic Revelation get better when paired with high-power creatures, and hydras have plenty of ways to get huge
At the same time, because it could establish a quick advantage on the board with threats like Frenetic Efreet or the hard-to-deal-with Wildfire Emissary, even light control elements could help the deck hold the advantage until it was time for a game-ending Fireball or Earthquake (often thanks to an end-of-turn Impulse)
Blue gets us access to counterspells, making interaction and removal versus the Atraxa players difficult to say the least, and impossible at its best
Swift Reconfiguration is a one-mana spell that can save your important creature from a sweeper, although youll then have to figure out a way to get it crewed later