I was wondering if you use Wish to recreate the effects of another spell and let's say I chose fireball. Would it be cast as a 3 level spell or could I choose for it to be cast at 8th level or even a 9th level? So can you use Wish to cast another spell at a higher level?

If you can could it be using a 9th level spell slot? Thanks!

https://twitter.com/JeremyECrawford/status/515864883737669632

Thanks but could I hear some more opinions?

Aside from the guy who wrote the book saying it. You would have the choice if you wanted it to be cast at any spell level you wanted. Wish for a fireball that does cantrip damage? Sure. Want to bum the entire d6 collection from the local dice goblin at the table by it being a 8th level fireball. Or anywhere in between. It is generally assumed you would do it at 8th.

Taking a snippet from the spell itself: 

"Wish is the mightiest spell a mortal creature can cast. By simply speaking aloud, you can alter the very foundations of reality in accord with your desires.

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."

However it does go on to state you can do more with it. such as being immune to a certain attack that you cannot risk again. You can also ask your GM if you would be able to cast it at 9th level. But it comes with a lot of bad things which should also be brought up.

Another snippet from the spell:

"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."

So to be safe stick with a max of 8th level. But if you want to risk it for something extra special. Hopefully you word that wish really good. And send the spell to the person who has to figure out what the heck to do. (if for other reasons, let the dm get time. Perhaps a week or two to figure out what they heck to do with it.)

It replicates spells up to 8th level.

You can make an 8th level fireball.

However, you are technically casting a 9th level spell, so Dispel / Counterspell will have to factor it as a 9th level spell.

Thanks that makes sense!