For four mana, you get to essentially draw another card each turn while sometimes making a token
The deck revolved around fairly low-power commons and uncommons, so Clear the Mind drafters could pick powerful and highly desirable spells early, knowing that the basic infrastructure for the deck would go late
If the target creature is an illegal target as Eriette's Lullaby tries to resolve, it won't resolve and none of its effects will happen
This allows you to trigger lots of powerful abilities on your turn as long as they are protected
The Sun & Moon era would later try different styles for their GX cards to great success, but these early sets did struggle with a reliance on this style which ended up rendering many of its Ultra Rare cards a bit lifeless
Green Rares: Scavenging Ooze $2.99 Thragtusk $1.99 Primal Command $0.99 Summoning Trap $0.75 Call of the Herd $0.49 Ulvenwald Tracker $0.49 As good as greens mythic rares are, the non-mythic rares are decidedly meh