The ability is not a mana ability
They can be played alongside high-cost cards in order to spend your extra ink and develop your board, they can get buffed by a Support character like Rolly and become a cheap way to trade up into bigger threats, and Lucky can discover them when you use his ability Good as New, making them more valuable in your deck than in your hand
With how absurdly cheap Cloud, Midgar Mercenary is to keep on the field, there's practically endless combo potential for the Buster Sword-wielding hero to unleash upon your enemies
Cruella de Vil, Fashionable Cruisier is your only real counter, but Launch can be used in a pinch too
Wizards of the Coast and Square-Enix confirmed several characters being featured as part of the collaboration, including Lightning, Sephiroth, and Kefka among others