COPY-CASTER

You study the differences in subtle inflections of verbal components, percise movements of somatic components, and physical properties of material components. The intricacies of the ways these components interact with the fabric of magic are your area of expertise.

Arcana Mastery
Starting at 2nd level, you become an expert on knowledge of the fabric of magic, known to some as the Weave. Your proficiency bonus is doubled for any Arcana check if you are proficient in it.

Copy Casting
At 2nd level, you have learned how to carefully observe the casting of spells and replicate these motions. When a spell of 1st level or higher is cast within 60 feet of you, you can use your reaction to make an Intelligence (Arcana) check to attempt to copy the spell. The DC is 10 + twice the level of the spell slot used to cast the spell. On a successful check, on your next turn you can expend a spell slot of the level the spell was cast at to cast the spell at that level.
When you cast a spell this way, this spell can be copied to your spellbook at any time within the next hour. If the spell isn't a wizard spell, it counts as a wizard spell when you cast it. Your spellbook can hold a number of non-wizard spells equal to twice your Intelligence modifier (minimum of 1). You can copy one spell this way per day, and the gold and time you must spend to do so is doubled.

Spell Secrets (modification of Lore Mastery ability)
At 6th level, you learn to augment spells in a variety of ways.
When you cast a spell with a spell slot and the spell deals acid, cold, fire, lightning, necrotic, radiant, or thunder damage, you can substitute that damage type with one other type from that list (you can change only one damage type per casting of a spell). You replace one energy type for another by altering the spell’s formula as you cast it.
When you cast a spell with a spell slot and the spell requires a saving throw, you can change the saving throw from one ability score to another of your choice. If the spell requires multiple saving throws, you can only change the ability score of the first. Once you change a saving throw in this way, you can't do it again until you finish a short or long rest.

Spell Stealing
At 10th level, you can attempt to interrupt the casting of a spell as you copy it, siphoning that arcane energy into your own casting. When you copy a spell with Copy Casting, you can force the original caster to make a saving throw against your spell save DC. The ability score for this is their spellcasting ability. If they fail, they fail at casting the spell and if you cast it on your turn it is cast at one level higher, still using the original level spell slot. Once you use this feature, you can't use it again until you finish a short or long rest.

Master of Magic
At 14th level, your spellbook can hold any number of non-wizard spells learned through Copy Casting.
This should have a second ability on top of this, let me know if you think of a good one.

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