I'm in a new high-level campaign which is a continuation of a previous one. I'm an 18th-level wizard, and our DM allowed us to have multiple simulacra at a time in the previous campaign. However, now I am able to cast 9th-level spells, including wish.
The description of simulacrum says:
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.
The side effects of wish:
The stress of casting this spell to produce any effect other than
duplicating another spell weakens you. After enduring that stress,
each time you cast a spell until you finish a long rest, you take 1d10
necrotic damage per level of that spell. This damage can't be reduced
or prevented in any way. In addition, your Strength drops to 3, if it
isn't 3 or lower already, for 2d4 days. For each of those days that
you spend resting and doing nothing more than light activity, your
remaining recovery time decreases by 2 days. Finally, there is a 33
percent chance that you are unable to cast wish ever again if you
suffer this stress.
What if I create 2 simulacra (expending 7th and 8th-level slots) and order them to cast a wish for me? Who will be affected by the side effects?
Best Answer
The above is taken from the D&D Adventurers League FAQ March 24, 2017, currently available here.
However, that stated, these rulings are for the balance and survival of Adventurers League, an organized play setting, and not explicitly the traditional table setting. Without explicit rulings like this on things the books don't cover, a nationally organized play association would not be able to run reasonable events with a common experience across all venues. Having a whole lot of "This DM let me do it at this event" isn't healthy to that ecosystem.
It is well understood by many players and DMs alike that rules as written for Simulacrum + Wish can be exploited for some serious imbalance in player agency and power: you can do anything you want without suffering the usual consequences. While I can't speak to the true intent of Adventurers League, this is likely why Adventurers League has made this decision despite there being no such restriction in the Player's Handbook to that spell combination.
By RAW it works because the Simulacrum is a separate creature, it just happens to have your resources and abilities.
By AL rules it doesn't work, because the Simulacrum is treated as you for the purposes of Wish.
Your DM has Rule 0, not even wizards can stop that!
Wizards doesn't have final say at your table. They give you the system, the basic foundations of the mechanical bits and pieces of your storytelling experience. Your DM can decide to use this ruling as an example of best practices and put it into practice in their game. Or they can decide that your game doesn't need the measures against Simulacrum + Wish synergy and allow players which earn those abilities/spells to be able to use them in that way.