Slimefoot aims for more of an Aristocrats theme (a deck that seeks to slowly deal damage to opponents and raise your life total when your creatures die), and can become very dangerous with all the Saproling support that exists across MTGs history
She's a land named Moon
Sometimes a card design just gets the mechanics, art, name, and flavor just right, and I think Fling definitely deserves to tick all of those boxes
The thought process was that ally colors should be easier to play as it matched the flavor of the color pie
Not only does having three or more opponents considerably increase the ceiling on the return here, but the proactive nature of multiplayer games makes it more likely that those opponents will be tapping out (at least outside of cEDH power levels)
Over time, this strategy has evolved, and many similar mechanics have been introduced in Magic: The Gathering