Spell Stealer

Spell stealers have learn how to absorb the weave energy of spells and send them back for their own uses. 

Arcana knowledge

At 3rd level when you choose this archetype, you gain proficiency in the skill arcana if you don't already have it. Additionally, your proficiency bonus is doubled for any ability check that uses arcana.  

Spell thief

At level 3, when you pick this archetype. When a caster you can see or hear within 120ft of you casts a cantrip or spell of 1st level, you can use a reaction to make a Constitution saving throw (DC equal to the spell save of the caster), on a failure the spell is cast off as normal. On a success, the cantrip or spell is sucked away into you and does nothing. You can cast this cantrip or spell once any time (DC equal to 8+profiency bonus+ your constitution modifier). Spells with a gold cost or consumable component automatically fail the saving throw. you can use this feature equal to a number of times equal to your proficiency bonus and can have a number of spells equal to your constitution score divided in half. At 8th level, you can pluck 2nd level spells. At 12th level you can pluck 3rd level spells. At 16th level you can pluck 4th level spells. and finally at 20th level you can pluck 5th level spells.

Smell of spells

At 9th level, your knowledge of spells has helped you recognize the smell of magic. As an action, you can spend 1 minute to attempt to identify magic within a 15ft radius. This feature works similarly to the Detect Magic spell. If you find magic, you can roll an investigation check to find what the type of magic is. If you cannot smell, this feature automatically fails. You can use this feature twice per long rest. 

Spell resistance

At 13th level, you're adaption to using spells has allowed you to gain resistance to spells you cast. when you cast a spell, you can use your reaction to gain resistance to what that spell was. An example being, if you cast fire bolt you gain resistance to fire but if you cast charm person you have advantage on charm saves. This resistance goes away when you cast a new spell and gain its resistance or if you take a short or long rest. This feature does not work if the spell cant give you resistance (such as healing word doing healing). you can use this feature equal to a number of times equal to your proficiency bonus.

Fast caster

At 17th level, you are able to cast spells in half the time. Alarm takes 30 seconds instead of 1 minute. Action spells become bonus actions but can't cast 2 action spells in a row and bonus action spells are not effected.