Base Class: Rogue
The Spell Thief specializes in stealing the spells of their enemies. Some were born with a knack for magic, but took a different path in life. Others have spent their career stealing and selling scrolls. Their exposure has given them an innate knowledge of how arcane magic functions and their quick fingers allow them to copy some of the most basic spells. With time, a Spell Thief learns to turn a caster's own magic against them and turn a profit off the magic they collect. In the world of Red Sword, nothing is safe from a determined thief.
A Trick of the Trade
At 3rd level, a Spell Thief may choose one cantrip from the Wizard spell list. This cantrip may use your dexterity as the casting ability.
A Quick Study
Spell Thieves trade in magic. So many things have passed through their hands that they have become attuned to the arcane. A Spell Thief may identify and use any scroll whose spell level is equal to or less than that of their proficiency modifier. Any scrolls used with this class feature will replace the existing casting stat, if any, with the Spell Thief's Dexterity modifier.
Arcane Pickpocket
Beginning at 9th level, a Spell Thief is able to feel the movements of the magic in the air. They can steal this magic the same way they steal a coin from a purse. Using your reaction, a Spell Thief can interrupt a spell being cast within 60 feet of them. If the spell's level is equal to or less than your proficiency modifier, it has no effect. If a spell level is higher than your proficiency, the Spell Thief must make an ability check using Dexterity + Proficiency. The DC of the check is 10 + the spell's level.
If a spell is successfully interrupted, it is stored in the Spell Thief's mind. During a short or long rest, this spell can be transcribed to a scroll using ink and parchment. This scroll cannot be used by anyone except a Spell Thief. Only one spell can be kept in memory at a time.
This feature can only be used again after a short or long rest.
The Living Arcane
At 13th level, a Spell Thief is so familiar with the magics of the world that they are able to feel it all around them. They become partially magical themselves. The Spell Thief may cast the spell Detect Magic at will once per short rest.
Any scrolls or cantrips that are cast using your Dexterity as the casting modifier may gain the benefits of Sneak Attack. All other rules for Sneak Attack apply. If a spell hits multiple enemies, the player may only apply Sneak Attack damage to one of them.
From Your Lips to Mine
At the apex of their skill, a Spell Thief may turn a spell back on its caster. When a spell is interrupted using the Arcane Pickpocket feature, a Spell Thief may forego storing that spell in their memory and may instead cast it immediately as though it were a scroll.
Additionally, your knowledge of magic has become so robust that a Spell Thief may cast any scroll, regardless of the spell's level.