So, you would have had cards with the type Enchant Creature instead of Enchantment Aura and enchant creature as the text
Green is the creature color (and thus the color that most benefits off of having creatures) and has life gain
Basically, it's everything about Magic I love all wrapped up into a four-mana artifact
Fact or Fiction became such a powerhouse that it became an anagram for Vintage - "EOTFOFYL" which stood for "End of Turn, Fact or Fiction, You Lose." It led to dominant new decks in Vintage (such as a mono-Blue build called "BBS" for Blue BS which led to Morphing) and was ultimately restricted
Its status as a sought-after alternate art card makes it a centerpiece in many OP-01 collections
If that wasnt enough, Yarus not only slots into all manner of face-down decks as a card draw engine, but also does his best impression of recent green recursive tech like Yedora, Grave Gardener