Quote Originally Posted by JLandan View Post
Not additional spell slots beyond those granted by caster levels. Nor are additional extra attacks beyond those granted by class levels. Those would be meta-game, not in-game. The spell description is explicit about what it can do. None of it involves meta-game knowledge or core rules changes. Suppose the wish was to roll a d30 instead of a d20? Should that be allowed? Or automatic success for all saving throws? Or to instantly advance ten levels? What if the wish was for ownership of the DM's car?

Wish alters reality in-game, not meta-game.

It can sometimes be difficult to tell the difference between meta-game and in-game. A good question to ask is who the wish is for, the PC or the player? You may say spell slots and extra attacks are in-game and allow such, perhaps with some crazy rationalization. I would not.
But isn't there a literal in-game Boon from the DMG that grants an additional 9th level spell slot? Wouldn't that satisfy your condition for it being in-game and not meta-game since you consider rerolling a d20 to be an in-gams thing and not a meta-game thing?

I mean, its not exactly the slippery slope you're making it out to be. Though if a player were to ask to roll a d30 instead of a d20...I might allow it for a single roll provided they have a physical d30 on them. XD If only because that would be a very interesting dice to see.