So I’m planning a blood war spell Jammer Champaign that follows a lot of themes from Seven Deadly Sins (SDS) but isn’t a true SDS game. Examples I want to incorporate the sacred treasures as legendary weapons (I found a set on DM guild but I will tone them down to be around the same power level as other legendary items) and I want to incorporate the 10 commandments as Devil generals (only this is how Asmodeus will bolster the ranks as it all serves to stop the Abyss and the blood war)

Outside of the home brew weapons and commandments (make these a feat each I think), and the creatures below I want to only use 1st party or 3rd party stuff that’s already available on BBG (ex Critical role stuff).

But now to the premise:

Asmodeus comes up with a new way you bolster his rank and splits a portion of his divine spark to create the 10 commandments.

Each commandment will be immune to the effects of other commandments but not their own.

While he gave some of the commandments to actual devils he also used them as means to convert other creatures into the fold. I decided one creature will be an Elder Brain that is cursed to be loyal to Asmodeus and he creates new infernal Illithid (still in progress how I want to combine devils and mind flayers). Another one will be one of his twin sons, both fire genasi (he created them with a fire elemental as a means to bypass barriers trapping fiends in lower planes. Only they are not demi gods due to spark removal)

What I’m asking for is what other monsters are recommended. I’m looking specifically for ones that create new monsters. I know Vampires and Lycans do this but I don’t want to use either

Well the most basic monster that makes more of itself, is the Shadow. If you want weirder stuff, the claw attacks from Red Slaad and Blue Slaad infect their targets with Slaad Tadpole eggs that eventually burst out of the host, birthing new Slaads. While you were less interested in Vampires generally, you may want to consider Vampirates, as they are sorta fun and Spelljammer-y. And speaking of, since you had interest in messing around with weird Mind Flayers, maybe consider the Vampiric Mind Flayer. It doesn't technically make more of itself....unless you want it to. Other than that, the Nergaliid from the Wildmount book is a devil that comes to mind, and Sword Wraith Commanders can summon some friends as well.

Thank you. I really like some of those.

now before I assign each creature a commandment I should list what they are and mechanically what they do so:

Faith; “Anyone who shows a lack of faith will have their eyes set ablaze.” Mechanic: 

Love; “Anyone who holds hatred in their heart will be unable to afflict harm on anyone else.” Mechanic:

Pacifism; “Anyone who kills will rapidly have their own time stolen away, causing them to rapidly age and die.” Mechanic:

Patience; “Anyone who shows intolerance of pain will be inflicted with further pain.” Mechanic:

Piety; “Anyone who shows their back to the wielder will become an obedient slave of the Lord of the Nine and by extension, the commandment's holder.” Mechanic: 

Purity; “Anyone who conducts impure deeds will be inflicted with illness.” Mechanic:

Repose; “Anyone who fights without rest will have their power locked away” Mechanic:

Reticence; “Anyone who expresses hidden feeling and/or emotions will be rendered unable to speak.” Mechanic:

Selflessness; “Anyone who holds desire from another person will lose their memories, emotions, and sense of self.” Mechanic:

Truth; “Anyone who lies or goes back on their word will be turned to stone.” Mechanic: