Check out this guide to help you prepare for Prerelease
Like most Magic: The Gathering cards, the value of Teferi, Mage of Zhalfir depends on a few consistent factors: its rarity, the printing and finish (regular or foil), its physical condition, and the set it was printed in (Final Fantasy: Through the Ages)
Equip variants or equip abilities with restrictions, like the "equip legendary creature" ability of Wrecking Ball Arm, are still equip abilities, and their costs will be reduced by Cloud's last ability
You also get to generate two lore whenever one of your characters prevails
You can also try to get a Support character like Huey or Dewey out on turn two or three to ensure that your four-cost character can banish whatever Maid Marian targets, but a Maui, Soaring Demigod will almost always do the trick