Here's the enemy list from my near photographic memory, classified into enemy, mini-boss, and boss.
Enemies
Marionette (knife, blade, and shotgun variants)
Bloody Mari
Blade (small and large)
Frost
Plasma
Sargasso
Nobody
Beezlebub (blue flies and green beetles)
Sin Scissors
Sin Scythe
Fetish
Mini-Bosses
Death Scissors
Death Scythe
Shadow
Kyklops
Bosses
Phantom
Griffon
Nelo Angelo
Nightmare
Mundus Angel Form
Mundus Volcano Form
Mundus True Form
That's all of them, I think.