(10/14/2022) For Soundwave, Superior Captain's abilities, if a spell you are casting has an in its mana cost, use the value chosen for X to determine its total mana value
Let's take a look at a list
On one starry hand, you can ignore the keyword completely and cast them as enchantment creatures

Adventurer's Airship Adventurer's Inn Aettir and Priwen Balamb Garden, Airborne Balamb Garden, SeeD Academy Baron, Airship Kingdom Blitzball Buster Sword Capital City Clive's Hideaway Cooking Campsite Crossroads Village Eden, Seat of the Sanctum Elixir Excalibur II Forest Genji Glove Gohn, Town of Ruin Gongaga, Reactor Town Guadosalam, Farplane Gateway Insomnia, Crown City Instant Ramen Iron Giant Ishgard, the Holy See Island Jidoor, Aristocratic Capital Lindblum, Industrial Regency Lion Heart Lunatic Pandora Magic Pot Magitek Scythe Midgar, City of Mako Monk's Fist Mountain Plains PuPu UFO Rabanastre, Royal City Relentless X-ATM092 Ring of the Lucii Sharlayan, Nation of Scholars Starting Town Summon: Bahamut Swamp The Gold Saucer The Masamune The Regalia Treno, Dark City Ultima Weapon Ultima, Origin of Oblivion Vector, Imperial Capital Wastes Windurst, Federation Center World Map Zanarkand, Ancient Metropolis