Like most Magic: The Gathering cards, the value of Ultima, Origin of Oblivion 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)
Kill creatures (yours and your opponents) to make him as big as possible
Once your cards are graded, PSA ships them back to you
It's a cheap creature that sits on the board growing slowly larger, and thanks to all our high mana cost spells, it can spit out an absolute ton of mana over the course of a game
Once we had Priest of Titania creatures, it seemed natural to have Priest of Titania spells: (Wirewood Pride, for example was called "Giant Growth of Titania" in design.) The one-shot spells then led to permanents that trigger a tribal effect: Its interesting to note that Elvish Guidance got created because we wanted to find some way to get the Priest of Titanias effect into the set
When this Aura enters, if it's on the battlefield, it loses "enchant creature card in a graveyard" and gains "enchant creature put onto the battlefield with this Aura." Return enchanted creature card to the battlefield under your control and attach this Aura to it