Kenku Sorcerer

Dark feathers swirling in a magical breeze, the kenku raises her hand and makes precise motions with her fingers. The lyrical voice of an elf springs from her throat, and a moment later a bolt of shimmering ice blasts from her hand, knocking the oncoming orcs to the ground. 

Kenkus are cursed with no real voice and no real creativity of their own, so when one manifests the rare gift of magic, it is almost a tragic loss of potential. But some learn instead to harness their other gifts in order to find a new path forward. 

Kenku sorcerers can use their talent for mimicry to copy the magic of other spellcasters, matching their movements and speech patterns to replicate other spells exactly as they were cast. But this talent is hamstrung by their curse, as the sorcerer is generally unable to modify the spell after it has been copied - though a few skilled kenku learn to use their magical strength to overcome this limitation...

Arcane Understudy

You have spent your life studying and copying the magics of other spellcasters. When you choose this origin at level 1, you gain proficiency with the Arcana and Performance skills if you don't already have them, and can add double your proficiency bonus to checks made with these skills. 

Arcane Mimic

Starting at level 1, you have the ability to learn to replicate the spells cast by other spellcasters. When you witness another spellcaster cast an arcane (but not divine) spell, you can use your reaction to make an Arcana skill check to attempt to learn how to copy the spell. The DC for this save is equal to the spellcaster's spell save DC plus the spell's level. 

If you succeed on the check, you learn how to cast that spell and can cast it in the future using your spell slots, assuming you have spell slots of the relevant level. 

However - due to your kenku curse, you are unable to modify the spell after it has been copied. Thus, you are only capable of casting the spell exactly was it was cast previously. This means, for example, that if you copy a spell being cast on three targets, you can only cast it on three targets. A copied fireball cast at a distance of 45 feet can only be cast by you at a distance of 45 feet. An copied illusion spell will always produce the same illusion. You can only cast a copied spell using the same spell slot level it was originally cast with, and you cannot use your metamagic abilities on copied spells. Note that as the copied spell uses your magical strength, it utilises your spell save DC, and ranged attack rolls and damage dice are rolled as normal, not copied. 

Modify Copy

At level 6, your magical strength allows you to push through the restrictions of your kenku curse, for just a moment. You gain access to a new metamagic option when you cast a copied spell. You may use 1 sorcery point during casting to modify one of the following traits of the copied spell, within the limits of the original spell: duration, range, area, number of targets, verbal/material/somatic components (substituting material components which are consumed for those of equivalent value)  or damage type (if the original spell has access to different types of damage, such as Chromatic Orb). You can use up to 3 sorcery points to modify multiple aspects of the spell at the same time.

Mage Reader

Your talent for studying the motions of spellcasters has taught you to read their intentions in their body movements. From level 6, you have advantage on Insight (Charisma) and Perception (Wisdom) checks against any creature who can perform magic, and you gain the ability to read lips if you can see a creature's mouth and it is speaking a language you understand. 

Studied Counterspell

Your skill at reading the actions of other casters has grown to the point where you can copy them and interrupt them at the same time. From level 14, you can spend 2 sorcery points to cast Counterspell or Dispel Magic as a 3rd level spell, and can increase the spell level for an additional sorcery point per spell level. If you successfully counter a spell in this way, you can roll Arcana to copy it as it would have been cast. If you successfully dispel an effect, you can roll Arcana to copy the spell that created it (to replicate the same effect). The DC for either of these copies is the 10 + the spell's level. 

Mastered Copy

At level 18, your eye for copying magic has grown to the point where you can learn the intricacies of a spell as well as its original casters, using your sorcerous strength to overcome the limitations of your kenku curse. If you have successfully copied the same spell three times (in any combination of spell levels, ranges, targets, casters, etc) you master it. You can spend 2 sorcery points to cast a mastered copy using an appropriate spell slot. This spell is cast as though it is a known spell for you, allowing you to cast it in any way permitted by the original spell's parameters. You can utilise any of your metamagic abilities on a mastered copy.