genie warlocks make this spell absolutely broken lol

Quote from AdmiralDave >>

What does the simulacrum do if the caster dies?

 There is a simulacrum in an official source adventure

 that lives on explicitly after it's caster dies. It actually seeks a "life spark" to make itself real after it's master dies. It's a significant part of the story.

So to do a inf chain of simulacrum 1st you’d need to have access to the wish spell and add it into your spell book and have the simulacrum spell of course. 2nd cast the spell using wish or the 7th level slot it won’t matter you’ll be spending a ton of money by the end of this anyway [I’d just bite the cost with 7th slot loss]. Then make 9th level spell scrolls with wish and repeat this till you’re out of money. Wait a day so you get all spell slots back. Finally with all the scrolls in hand have your sim make a sim of you then their sim make a sim of you etc etc till all the scrolls are used up. Keep in mind the chain of command since if at any point one dies in the middle of the command chain that simulacrum no longer has to follow your order unwaveringly.

IMHO any GM that allows infinite simulacrums is embracing slapstickery. Even if the rules are not explicitly against multiple simulacrums, I feel it will break immersion. In my campaign high-level casters use simulacrums as proxies in dangerous situations, for example BBEG dealing with the PC:s. If the negotiations go badly and the PC:s choose the murderhobo solution, the simulacrum can cast Time Stop and hide 2-5 Freezing spheres in it's pockets. The PC:s can then kill the simulacrum and as they pickup the remains of ice and snow, the spheres will explode for 40D6.

The fact that the simulacrum needs herbs and minerals worth 100 gp per hip point lost to be repaired means that repairing a simulacrum is extremely inefficient. By the time you heal 15 hit points on it you might as well have just cast the spell again and get a new one. 

Why is this spell not Transmutation? I'd be tempted to allow clay or some other material as a component instead of just frozen water. ice and snow don't exist on every world.

As others have stated you'd have to be within touch of a terrasque for twelve hours but... what if a bdub made his base in an arctic laboratory where he found a frozen terrasque (or even conquered and froze it himself along with a library of scary creatures) and used its frozen being to birth an army of terrifying knock off creatures 

Quote from SpaceCactuss >>

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!

 

 No, not anything, just a beast or a humanoid.  A tarrasque is neither.

My DM made the BBEG have this, and use it for the "final" boss fight. I am very sad.

Is there an official ruling on what happens if the original creature has body parts replaced by magic items? Ersatz Eye, Eye and Hand of Vecna, etc. I wouldn't expect the item to be duplicated, but it's unclear whether or not a mundane copy would be created and how it might function. I suspect the answers will be table specific, but any official guidance would be useful.

Could you use wish, to cast Simulacrum, and then have your Simulacrum, cast wish? And if so if it rolled under 33, could you just recast it and it has wish again?

if i use wish to make this would my Simulacrum also have wish? and if so seems very much a headache for DMs, like ok Simulacrum( cast wish, he cant use wish again, thats cool make a new one, or bc i used a 9th lvl spell it wouldnt have a 9th lvl spell?

live its best life

For those speculating on using Wish to abuse this to create essentially an infinite amount of copies of yourself... Well, if you want to abuse this spell by just going off of RAW...
A couple of things:

1. The spell rules state: and is formed without any equipment. Your simulacrum has no spell focus, nor a spell book to cast Wish from.
2. The simulacrum is an illusory duplicate and the illusion uses all the statistics of the creature it duplicates, except that it is a construct. Wish RAW states: Wish is the mightiest spell a mortal creature can cast. Since the simulacrum is neither a mortal, nor a creature, it cannot cast Wish.
3. Nowhere does it say that it has all the spells you have either, it just has your spell slots, that's it.
4. Back to wish, the RAW in wish state the following as well: The GM has great latitude in ruling what occurs in such an instance; the greater the wish, the greater the likelihood that something goes wrong. This spell might simply fail, the effect you desire might only be partly achieved, or you might suffer some unforeseen consequence as a result of how you worded the wish.
   This gives the DM complete freedom on how to rule on you trying to abuse this trick, any argument you make to the GM is useless at that point.

And yes, I know that some people would argue about point number 2 and say: "but yea, they mean that gods can cast more powerful spells and magic than Wish."  Well I raise you this: you want to abuse RAW to get a one up over your DM? He can get a one up over you... Any argument similar to the example above is pure RAI, not RAW.
Now, if we allow RAI... ooh baby, you have even less of a foot to stand on... And even less if you go with Rules as Interpreted (instead of intended)...

What I'm getting at is this, you can try to break the game, but if your DM says no, it's no, and in this scenario the RAW has his back.

Quote from LeXtruX >>

The spell rules state: and is formed without any equipment. Your simulacrum has no spell focus, nor a spell book to cast Wish from.

 
It doesn't need any.  Wish only requires verbal components.

Quote from LeXtruX >>

The simulacrum is an illusory duplicate and the illusion uses all the statistics of the creature it duplicates, except that it is a construct. Wish RAW states: Wish is the mightiest spell a mortal creature can cast. Since the simulacrum is neither a mortal, nor a creature, it cannot cast Wish.

 
Sorry to be blunt, but that makes no sense.  A mortal creature being able to cast a spell does not inherently have anything to do with whether an entity that isn't a mortal creature can cast it.  That's like saying, "70 kilograms is the most weight an average adult human male can lift.  Therefore, an industrial crane cannot lift 70 kilograms, because it is not an average adult human male."

And by the way, in the context of the rules of D&D, a construct is a creature. This spell's description even says that the duplicate is a creature.  And arguably, it's even more mortal, since it has half HP and no death saves...

Quote from LeXtruX >>

Nowhere does it say that it has all the spells you have either, it just has your spell slots, that's it.

 
"[...]Otherwise, the illusion uses all the statistics of the creature it duplicates, except that it is a construct."

Once again, in the context of the rules of D&D, a creature's statistics encompass all the mechanical information that governs how it functions in the game, where it may differ from other creatures.  That includes its spells known.

(Warning: Unnecessary rambling.  Not sure why I kept this next part.)

Quote from LeXtruX >>

Back to wish, the RAW in wish state the following as well: The GM has great latitude in ruling what occurs in such an instance; the greater the wish, the greater the likelihood that something goes wrong. This spell might simply fail, the effect you desire might only be partly achieved, or you might suffer some unforeseen consequence as a result of how you worded the wish.

This gives the DM complete freedom on how to rule on you trying to abuse this trick, any argument you make to the GM is useless at that point.

 
"in such an instance"

The "instance" that Wish's description is talking about is the case where the player makes up an effect.  One that is not duplicating a spell that is 8th level or lower, or any of the five specific other uses listed.  Therefore, duplicating a lower-level spell is not covered by the "GM has great latitude" clause.  RAW, the duplicated spell works, unless that spell's description says otherwise for the given situation.

Now don't get me wrong, the DM can make any number of house-rulings to counter such shenanigans as the clone army in question.  Indeed, as you say, if the DM says "no," it's "no."  All I'm saying is, the rules as-written don't have the DM's back in the ways you say they do.

Since the simulacrum is a construct created from a spell not a living creature with a soul it can simply be destroyed with a anti magic or dispel magic spell right?

THAT SPELL IS SOOOO GOOD!!

Steps to start a Simulacrum Chain

1. Hold a piece of equipment so that you can identify yourself as "Wizard Prime". This equipment will not be duplicated.

2. Cast simulacrum on yourself, burning a 7th level spell slot.

3. Give the following commands to your simulacrum:

a) "I command you to obey Wizard Prime, whose instructions take precedence over my own."

b) "I command you to cast Simulacrum on Wizard Prime using Wish."

c) "I command you to move out of the way and make space for future simulacra."

d) "I command you to give the exact same set of commands to any simulacrum you produce, including this command line."

Using this set on instructions, you will be able to produce a simulacrum of yourself every 20-30 seconds. (Wish only requires one action to cast but the "programming and automation" of simulacra will take a little longer). Assuming 30 seconds per simulacrum, you will produce 2,880 per day which will obey your commands. Any simulacra produced after the first 8 hours will have all their spell slots except for the 9th level slot which will be used to cast Wish. All simulacrum will have been commanded to obey you.

At any arbitrary point, you can interrupt this cycle after command "a" has been given. Countermand the instruction to cast Wish. This will allow you to reprogram the behaviour of future simulacrum. For instance, if you want access to unlimited wishes, you could initiate a slower production cycle where the Simulacra take the full 12 hour duration to cast Simulacrum, leaving their 9th level spell slot free. You can then instruct those Simulacra to Planeshift or Demiplane elsewhere to perform risky custom wishes. The biggest issue in terms of action economy is how well you are able to instruct and command your simulacrum army. It may be worth slowing the duplication process and implementing better "AI".

Ok then, because no one seems to really be talking about this. Depending on the race you play, a player can in fact not be able to cast this on themselves. Such as some of the new races in Spelljammer like the Slime people, some of the Fey races, and so on. Because of the limit to Beast and Humanoid, if you play an exotic race you very well may not be able to cast this on yourself.
In this cases I would suggest finding a good ally you can copy.

Does it have hit dice, can it use hit dice to heal itself? Can it get hit dice back on a long rest?