Theres a ton of scope for mixing and matching not only the Final Fantasy characters, but the rest of the Magic: The Gathering multiverse, including the crossovers
Only killing nonblack creatures does make it a bit narrow, but it makes up for it by allowing you to tap out to develop your board and still have interaction up to prevent your opponent from developing theirs
Sentinel Spider: My cube loves Spiders

Even if this card is pretty useless, it screams Cumly Cube Grim Tutor: tutoring is a small part of Cumly Cube but very important in the right decks Growth Spasm: offers ramp, mana-fixing, and supports the Eldrazi creature type Hymn of Rebirth: offers reanimation in green and white instead of its typical color, black Ice Storm: land destruction is a small part of Cumly Cube but a necessary balance, and not usually in green Jace's Triumph: there are Jace planeswalkers in Cumly Cube Mana Vapors: a strange tempo card that fits the ethos of Cumly Cube Many Partings: offers mana-fixing and food Migratory Route: offers mana-fixing and supports the Bird creature type Obzedat's Aid: offers reanimation in black and white Ordered Migration: supports the Bird creature type Raise the Palisade: supports all creature synergy decks Resourceful Return: a more situational and odd piece for black graveyard decks and artifact decks Ribbons of Night: offers direct damage in black instead of its typical color, red Rise of the Witch-king: a more situational and odd piece for reanimator decks Riveteers Confluence: similar to a charm Safewright Quest: offers slight mana-fixing in green and white Solve the Equation: tutoring is a small part of Cumly Cube but very important in the right decks Sweep the Skies: supports the Thopter creature type Temporal Machinations: supports artifact decks Unnatural Restoration: supports proliferate decks Urborg Repossession: a more situational and odd piece for black graveyard decks

If either face has a color indicator or basic land type, those are also considered.
Ferocious in her youth, Iymrith has grown more philosophical and even whimsical as she ages, but she has not lost sight of her quest for transcendence