Choosing from the entire list of non-creature spells means we have almost limitless choices available, but usually the best picks are effects that support a creature-combat plan (like combat tricks or defensive interaction), or which generate resources to fuel more spellcasting
Any time you can introduce Monarch into the game, I happily encourage you to, as it promotes combat and politics like almost nothing else
Legendary Creature Angel Nightmare Avatar Flying Super Nova As this creature transforms into Sephiroth, One-Winged Angel, you get an emblem with "Whenever a creature dies, target opponent loses 1 life and you gain 1 life." Whenever Sephiroth attacks, you may sacrifice any number of other creatures
This means your opponents may want to think of some other way to get rid of this snow beast besides challenging it head-on
Thus, there are only a few in circulation
Commander loses part of its soul and ethos without the ability to build fun, weird, flavorful decks