Tier 1 (Level 4): Choose 1

Chosen
Sturdy Feathers

Lady Cluckington's AC increases by +1, and she gains resistance to one damage type of your choice (cold, fire, or lightning). You can change the damage type during a long rest.
Fleet of Foot

Lady Cluckington’s speed increases by 10 feet, and she can take the Dash action as a bonus action once per short rest.
Keen Eyes

Lady Cluckington gains proficiency in Perception and has advantage on Wisdom (Perception) checks. Additionally, Pippin has advantage on initiative rolls while mounted.

Tier 2 (Level 6): Choose 1

Protective Instincts

When a creature within 5 feet of Lady Cluckington attacks you, she can use her reaction to make an opportunity attack against that creature. Additionally, Lady Cluckington can take the Help action as a bonus action.
Aerial Grace

(Prerequisite: Fleet of Foot)

Lady Cluckington gains a fly speed of 30 feet, but she must land at the end of her turn or fall. She can hover at a height of up to half of her fly speed for up to 1 minute once per long rest.
Intimidating Presence

Lady Cluckington can use an action to let out a terrifying screech. All enemies within 15 feet must make a Wisdom saving throw (DC = 8 + your proficiency bonus + your Charisma modifier) or be frightened for 1 minute. They can repeat the save at the end of each turn. Once used, this recharges on a short rest.

Tier 3 (Level 8): Choose 1

Iron Will

Lady Cluckington becomes immune to being charmed or frightened, and gains proficiency in Wisdom saving throws.
Razor Beak

Lady Cluckington’s natural attacks now count as magical for overcoming resistance, and deal an additional 1d4 slashing damage. Once per turn, when she hits with a beak attack, the target must make a Constitution saving throw (DC = 8 + your proficiency bonus + her Constitution modifier) or bleed for 1d4 damage at the start of their next turn.
Loyal Bond

You and Lady Cluckington share a telepathic link within 100 feet. Additionally, when you cast a spell of 1st level or higher that targets only yourself, you can choose to have it affect her instead (if beneficial)

..

Tier 4 (Level 10): Choose 1

Feathered Shield 

(Prerequisite: Sturdy Feathers)

As a reaction, Lady Cluckington can spread her wings to grant you and herself half cover (+2 AC) against one ranged attack. Additionally, once per long rest, Lady Cluckington can cast shield on itself or you.
Wind Walker 

(Prerequisite: Aerial Grace)

Lady Cluckington’s fly speed increases to 50 feet and she no longer needs to land at the end of her turn. She can also carry one additional Medium creature while flying.
Pack Leader

(Prerequisite: Intimidating Presence)

Lady Cluckington’s frightening screech now affects creatures within 30 feet, and frightened creatures have disadvantage on attacks against you and her. Additionally, Lady Cluckington can cast animal friendship once per long rest.

Tier 5 (Level 12): Choose 1

Stalwart Companion

Lady Cluckington’s hit point maximum increases by 20, and she gains advantage on death saving throws. When reduced to 0 hit points, she can choose to drop to 1 hit point instead (once per long rest).
Thunder Wings

(Prerequisite: Wind Walker)

When Lady Cluckington takes the Dash action while flying, she can create a sonic boom. All creatures in a 15-foot radius must make a Constitution saving throw (DC = 8 + your proficiency bonus + her Constitution modifier) or take 2d6 thunder damage and be deafened until the end of her next turn.
Apex Predator

(Prerequisite: Razor Talons)

Lady Cluckington’s attacks score critical hits on rolls of 19-20. Additionally, when she reduces a creature to 0 hit points, you both regain hit points equal to your proficiency bonus.