Wish states:
The basic use of this spell is to duplicate any other spell of 8th level or lower. You don't need to meet any requirements in that spell, including costly Components. The spell simply takes effect.
If I choose to duplicate Magic Missile do I create 3 darts (level 1), 10 darts (level 8), or 11 darts (level 9)? Or can I choose how many to create from some range?
In other words, what is the level of the spell slot "used" by the duplicated spell?
Just to be clear, when casting wish you only ever actually use a 9th level slot.
When you cast wish you get to decide what level the resulting spell is cast at per Jeremy Crawford:
A spell you duplicate with wish can be cast at a higher level, as long as that level is no higher than 8th.
8th level is the highest level you can cast the spell at because wish can only duplicate a spell of 8th level or lower.
See this sage advice:
When Wish is used to duplicate a spell, can it be duplicated at a higher level? For example, a 7th level Banishing Smite to bypass Limited Magic Immunity.
-> A spell you duplicate with wish can be cast at a higher level, as long as that level is no higher than 8th.
You still expend a 9th-level slot, of course.
The slot consumed by casting the spell Wish will always be a 9th level slot.
The effect of the spell you duplicate can be of any level no higher than 8th level.
See relevant Sage Advice and Jeremy Crawford Tweet
A spell you duplicate with wish can be cast at a higher level, as long as that level is no higher than 8th.
