The fair bucket is the largest, containing cards that are efficient and powerful, but that have a lot of redundancy within the Cube, such as Lightning Bolt, Counterspell, Llanowar Elves, cheap creatures meant for combat, and even big finishers like Frost Titan
Doing so was optional, but a bunch of artists played along: David "Help Me" Martin (on Aesthetic Consultation because the artist was being crushed in the art) Heather "Erica Gassalasca-Jape" Hudson (on Artful Looter
Lutri, Pauper Otter's companion restriction cares about the color of a card's expansion symbol, not its rarity
The ones that aren't on the Reserve List were never reprinted in a later set and thus brought into Modern
Leyline of Hope Lifegain payoffs and anthem effects are oversaturated, and not every lifegain deck even cares about pumping its creatures
The two remaining good options are Peri Brown and Romana II