D&D 5E An idea for Wish

[DEFCON 1]

Seems fine.

If you feel it is necessary or a positive for your game, then do it.

 

[Li Shenron]

*Every wizard or sorcerer gains wish as an extra spell slot at 18th level. It is not available at 17th level.

and/or

*Every wizard or sorcerer gains greater wish, as a "10th level spell," at 20th level. Greater wish allows all spells, including 9th level, to be duplicated.

The first one doesn't change much. Instead of probably the Wizard getting Wish at 17th level, she certainly gets it one level later but for free.

The second one requires a clarification: how does the Wizard cast a 10th level spell, since there are not 10th level slot? I assume you also want to give her one 10th level slot (usable also for other heightened spells) or otherwise just let her cast Greater Wish 1/day. Either way, this is a free boost (i.e. effectively a second 9th-level spell per day) to a character which at that level is already broken by having Wish in the first place.

Because let's face it... being able to cast ANY spell (even if excluding 9th level) from ANY class and ANY book at NO COST* is nothing but broken. The Sorcerer goes from knowing 14 spells to knowing 328 spells (PHB only) when they learn Wish. Sure, it's only 1/day and it costs your highest level slot. Still broken. It's the kind of capstone ability that throws balance off because anyway few gaming groups reach that level, and many who do reach it are probably bored at that point or getting near to wrapping the campaign anyway, so who cares if you've got Wish or a Deck of Many Things... have some wacky fun, then roll up some new 1st level characters.

*the design mistake with Wish is actually in this very precise spot: the DM's call for "something going wrong" when casting Wish should apply also to duplicating spells

I would have preferred there was Limited Wish...

Why, would you want to wrap up your campaign even at a level lower than 17th?

 

[77IM]

Increase the casting time to 8 hours. Suddenly wish will only ever be used when it's doing things that no other spell will do.

 

[Shiroiken]

Increase the casting time to 8 hours. Suddenly wish will only ever be used when it's doing things that no other spell will do.

I actually think more spells should have a longer casting time. Increasing Wish's casting time would solve a lot of problems, but I think the biggest issue is being able to straight up copy any existing spell 8th level and lower.

I had a major battle (and almost a campaign) ruined by a Wish that cast Heroes Feast, since they were expecting to face a lot of spiders and other poison effects (they were in the Vault of the Drow). My reworked version of Lolth dealt heavily in poison damage, so the first battle against her avatar was far too easy. I managed to hurt them, but not enough to inspire any fear of her. When they faced her Simulacrum in the Demonweb, it was nearly a TPK without that poison immunity. Needless to say, facing her true demon form low on resources (a long rest is impossible) was nightmarish for them.