Might not be using your own spell slots, but this is still using spell slots and the question wanted no slots.

This is an exploit that likely no reasonable table would allow but does work in theory so upvoted. Not sure about the 10th level thing though, whether you can upcast 9th lvl spell like this at all, but even if you do, the spell itself is still 9th level.

@AnnaAG It is explored in this question.

Are simulacra not 1/2 the original creature's level in 5e? Yeah who could have seen this exploit coming. lol

@Michael No, see the portion of the spell description I quoted: “the illusion uses all the statistics of the creature it duplicates, except that it is a construct.”

@ThomasMarkov right, it's just crazy to me that they would change that.

"Since the simulacra follow our commands", Technically, it follows commands of the caster of the spell, which isn't you for every simulacrum but one. While caster can make simulacrum be friendly to you, you will have one hell of chain of commands in the end.

@Revolver_Ocelot each simulacra can command it's subordinate to follow the commands of the origin, and never countermand a command from origin

I am tempted to induct this into our hall of cheese thread.

@Michael The simulacrum is half the original creature's hit points, not level. If each simulacrum created a new simulacrum by copying the previous one, an eventual copy would be at 0hp and unable to proceed. Also, if you cast the spell more than once any previous simulacrum is destroyed. The exploit here is getting each new simulacrum to cast the spell to copy you, so that each one has both a new caster and half your hp rather than half of the diminishing hp of another simulacrum.

@Kirt I think I've clarified the logic a bit, double check the steps for me?

@ThomasMarkov "...on the original caster" is a helpful clarification. I would add "...and to instruct the simulacrum created to obey the commands of the original caster." to Step 2. "Or can be instructed to do so" is good.

@Caleth Yes, but I think the implication there is "Follow the commands of the origin, never countermand a command from origin unless / until I tell you otherwise", since ultimately each simulacrum is loyal to its creator. Thus each one is still liable to charm, domination, etc. taking control of it and everyone downstream.

@Kirt Is that 1/2 the hp rounded down or up?

@ThomasMarkov if you use the modified simulacrum spell from Storm Kings Thunder you, the caster, can create an unbounded number of simulacra without running foul of the 1 simulacra/caster rule.

@illustro Which chapter/section is that in?

But to answer your question: Chapter 9 > Lyn Armaal > 21. library

@illustro Ah, so it allows the caster to cast sim again without destroying previous sims?

Yep it most certainly does! (Though it has an additional costly material component)

@Michael in 5e it's round down always unless explicitly told otherwise.