You shape an illusory duplicate of one beast or humanoid that is within range for the entire casting time of the spell. The duplicate is a creature, partially real and formed from ice or snow, and it can take actions and otherwise be affected as a normal creature. It appears to be the same as the original, but it has half the creature's hit point maximum and is formed without any equipment. Otherwise, the illusion uses all the statistics of the creature it duplicates, except that it is a construct.
The simulacrum is friendly to you and creatures you designate. It obeys your spoken commands, moving and acting in accordance with your wishes and acting on your turn in combat. The simulacrum lacks the ability to learn or become more powerful, so it never increases its level or other abilities, nor can it regain expended spell slots.
If the simulacrum is damaged, you can repair it in an alchemical laboratory, using rare herbs and minerals worth 100 gp per hit point it regains. The simulacrum lasts until it drops to 0 hit points, at which point it reverts to snow and melts instantly.
If you cast this spell again, any duplicate you created with this spell is instantly destroyed.
* - (snow or ice in quantities sufficient to make a life-size copy of the duplicated creature; some hair, fingernail clippings, or other piece of that creature's body placed inside the snow or ice; and powdered ruby worth 1,500 gp, sprinkled over the duplicate and consumed by the spell)
Besides the components, this is a crazy spell. If your in a snowy place, you could literally make anything! Get enough of it, it could become a Tarrasque!
if you are within touch range of a tarrasquefor 12 hours...
You don't need to be within touch range of a Tarrasque for 12 hours, just with pieces of it.
So maybe you found a bone, or somehow managed to get a piece it. Clip it's giant nails while it's sleeping.
I read this as you must be in range of the target which is to be duplicated for the duration of casting and you need a piece of the creature as a spell component. So.you would need to be in range of a tarrasque for 12 hours to dulpicate it.
Not to mention a tarrasque is not a beast or humanoid
This spell is broken. Cast it with yourself as the target, now you have two yous, the only difference is one has half the hitpoints. The simulacrum can definitely cast spells, as it says "nor can it regain expended spell slots." in the description. That means when you copy yourself, you now have a version that has all of the spells you normally have, it can just only use them once. That's not much of a problem, though, when you decide to make your copies make more copies, by casting Simulacrum on you again. Then, after leaving the original simulacrum in your demiplane or somewhere safe, you come back after a few weeks to have dozens of copies of you ready to fight in your adventures. Perhaps most usefully, they all have wish(if you have the spell) and you don't have to worry about them not being able to cast it again, essentially giving you 2 wishes a day for free.
OR
If you're 17th level, you also probably have access to wish and clone. Have your copies cast clone, then wish for the clone to mature instantly, or something. Kill the simulacrum, and now you have two simulacrums where there was only one. Rinse and repeat for exponential growth, until after a few weeks you have thousands of you's with probably no hitpoints(if they're casting on each other, then the hitpoints continue to half each iteration), but with all of your spells(we don't really care about the simulacrums that already used up their higher level spell slots.) Anyway, even if you don't want to break your game and have your DM tell you "no," this spell is still great.
20th Level Wizard 122 HP(an average HP) makes simulacrum 61 HP, who makes another Simulacrum 30 HP, Who makes another simulacrum 15 HP, Who makes another simulacrum 7 HP, Who makes another Simulacrum 3 HP, Who makes the final Simulacrum 1 HP. 7 Wizards all with access to 9th level spell slots. Each is not a copy of the original but a copy of the copy making it possible to maintain all the copies. With that level of magic power it could be amazing and disastrous all at once.
What does the simulacrum do if the caster dies?
True in theory, but a more effective application would be to have simulacrum 1 make a copy of the original wizard giving simulacrum 2 61HP, then simulacrum 2 creates a simulacrum of the wizard creating a third simulacrum with 61HP and so on without terminus.
The spell also requires a beast or a humanoid and as far as I’m aware constructs are not considered humanoids and so simulacra can’t be the target of the spell as they are considered constructs.
The only issue with this is how your DM interprets the Spell. If they read it RAW, a Simulacrum cannot copy itself because: "the illusion uses all the statistics of the creature it duplicates, except that it is a construct." If you create a Simulacrum (which is a construct) it cannot target itself as the target of the Simulacrum Spell because the spell needs to target a "beast or humanoid." But if your DM feels like copies making copies is awesome then they could make a ruling and say that it does in fact work.
The spell description doesn't account for this, but if I were ruling it I would say the Simulacrum could survive as long as it had HP remaining. It says "Untill Dispelled" and doesn't require concentration. I would also say a Dispel Magic could destroy it as well.
What if cast wish, and wish for a simulacrum of the tarrasque...
EDIT: Nope wait the tarrasque is a monstrosity... Dang it! I thought i broke D&D 5e!
The simulacrum would simply make a copy of you, the original.
12 hours per casting you could generate 2 simulacrums a day, ever day, forever.
No wonder rubies are rare and precious...
A lot of folks seem to be missing that a simulacrum does NOT have the spell slot that was used to create it, if the caster is copying himself.
(Official Ruling: https://twitter.com/jeremyecrawford/status/1011380498944311297?lang=en)
If you use your 7th-level spell slot to copy yourself, the resultant simulacrum is created with an already-expended 7th-level spell slot. If your PC has a 9th-level spell slot, he can instead use THAT to cast the spell, but then the simulacrum will have an already-expended 9th-level spell slot.
So between the required resources (either a 9th-level spell slot or plenty of snow/ice and powdered ruby,) the 12-hour casting time, and the fact that you can't copy a simulacrum (they're constructs, not beasts or humanoids,) this seems to eliminate most of the more outrageous abuses that some have suggested.
Except for the one where the wizard casts Simulacrum on themself, spends 12 hours on it and expends the 1500gp worth of material, then once created he tells the simulacrum to use it's 9-th level spell slot to cast Wish, use Wish as a 7th level Simulacrum spell on the same wizard. Sim1 now has expended a 7th and 9th level slot. Wizard takes a long rest while Sim 1 casts. Wizard now has all his spell slots back. Sim 1 finishes copy paste, Sim 2 is now a copy of Wizard with all spell slots. Orders Sim 2 to copy wizard with 9th level slot to avoid spending more money... Sim3 same orders... infinite copies of Wizard with 0 cost that are all missing only their 9th level spell slots...
To be fair, the simulacrums could just use a second 7th level slot to cast Simulacrum on the original wizard instead of a 9th.
The spell prevents them from regaining spell slots; that does not mean they cannot cast the same spell using a different spell slot.
The issue there is you have to spend either your SINGULAR 7th level spell slot to cast Simulacrum to start, and that if you are casting simulacrum more then once it requires 1500gp worth of dust EACH time. Unless you use Wish which removes the material cost of the spells you cast with it. Hence the 9th level spell slot, aka Wish.
Ah! I misunderstood folks reasoning for going to Wish.
This feels more like a transmutation spell, rather than an illusion.