They are the cement between the bricks or the gas in the engine
Red and white decks have the removal to milk value from the small dorks, green ones have to simply outclass everything else and so Experiment One is the only one drop in mono green that can ultimately pack enough punch for what this deck needs
Once a cheap creature that at worst cantrips by itself falls into your lap, you suddenly notice how many other cheap cards have higher toughness than power, like Thraben Inspector, Delighted Halfling, and Ajani, Nacatl Pariah
Boosters found inside the product can still contain Avatar's journey basic lands
Yu-Gi-Oh has been using 'Fiend' as a catch-all classification for demons, so it's actually a bit surprising that MTG doesn't actually have the 'Fiend' creature type anymore
Plus, being able to warp a game around your commander is good, and youll be drawing a bunch of cards while triggering sacrifice synergies