Quickleaf
Legend
I have changes that effectively nerf the Wizard (and a few other casters), but they are not attached to the class writeup:NOTE: If you wouldn't nerf the wizard... CONGRATULATIONS. But this may not be the thread for you. Also, we don't need to relitigate the question of martial versus caster supremacy. let's just take it as a given here, please.
Going with the presumption that in 5E D&D (of whatever particular flavor, 2014 or 2024 or ToV or A5E or whatever) and you wanted to bring thew wizard (and other full casters) down to ensure more parity with primarily martial characters, how would you personally, in your campaigns that you would actually play, do that?
There are a lot of potential options, from curating spell lists to instituting casting rolls to reducing the availability of cantrips and/or spell slots. So, what would you do.
For my part, my favorite implementation of most D&D tropes is actually Earthdawn from FASA in the early 90s, so I would take a page from that game. Spellcasting would require a check, with failure to cast exposes the wizard to potentially catastrophic attention by horrible entities from beyond space and time. It is important to note that this isn't just a "fumble chart" although that is a potential component. the real problem is that the wizard starts to collect corruption and attract the attention of the entities. There are lots of "horrors" in D&D that can play the part, depending on the flavor of magic. Magic is allowed to remain powerful, but wizards have to be careful. The more you cast, the more you roll, and the more you roll, the more likely you are to fail. Note that this system also allows the wizard to set up a small number of "safe" spell in matrices, which adds an element of important decision making regarding which spells to safely prepare.
What would you do?
1) Changing (nerfing) certain specific spells that are problematic or overpowered (e.g. removing the "force field" component of the new Leomund's Tiny Hut OR reintroducing the risk of "backdraft" from Fireball).
2) Including more situations specific to the adventure / scene / environment that make magic risky or difficult (e.g. stinging insects that disrupt Concentration OR city watch that is biased against spellcasters OR an elemental engine that causes all fire/lighting/radiant magic to conjure hostile elementals).
3) Revise monsters to greatly reduce "Resistance to nonmagical bludgeoning, piercing, and slashing", and instead increase the prevalence of unique resistances...especially toward certain types of magic (e.g. charming the fey causes its charmed commoners to suffer psychic damage OR as a reaction the shadow spider can intercept teleporting casters, causing them to appear next to the shadow spider, and it makes a bite attack against them).
I've introduced Roll-to-Cast for my sorcerer variant, and while it's fun, the introduction of two points of failure – the Roll-to-Cast and the Attack or Save – is not the best design. That's a key difference between "Magic as Skill Check"/Roll-to-Cast in OSR games vs. in 5e – the greater amount of rolling in 5e can make this contribute to combat drag & can feel punitive to players. This is why I ended up revising my Roll-to-Cast sorcerer variant so that most of the results of the Roll-to-Cast are "you cast the spell, but this drawback also occurs..."