What would a schema look like for setting up tables for RPG character creation restrictions?
There's not a specific schema name for what you're trying to achieve but there are two ways you can go about achieving it depending on which database management system you end up using.

You can create one linking table for each combination of values. Every legal combination will get it's own row, and have a foreign key field of the id of each base table that it's linking together. This is generally known as a dimension combination table.

You can alternatively look into having a more denormalized table that stores each instance of the character that's been selected, with foreign key refencing fields to each id of the base tables, with a composite constraint on what value combinations can be entered in each field. (The availability of this kind of complex constraint feature will be dependent on the database system you use.)