Familiars are Fey, Celestial or Fiends depending on their origin when being summoned or bonded to their wizard. You are your choice of those creature types, coming from your ancestry.

Small.

30 feet.

Your nature as a Familiar moves you towards wanting to discover new things. You have proficiency in the Perception or Investigation skill.

Your Familiar lineage gives you a special sense to perceive magic through your smell. You know the Detect Magic spell and you can cast as many times as your Proficiency Bonus without spending a Spell Slot. Moreover, when you cast this spell, you can do so without any components, and you know if a creature within the range has the Spellcasting, Innate Spellcasting or Pact Magic trait, feature or action.

Your Familiar lineage makes it so helping others comes easier for you. You can take the Help Action as a Bonus Action.

You have Darkvision with a range of 60 feet.

You descend from a specific species of familiar of your choice, which determines your appearance and additional traits.

Felis

You descend from a feline familiar lineage, such as a cat. As a Felis, you gain the following traits.

Purrsuasion. When you roll a Persuasion check, you can give yourself advantage. You can do this as many times as your Proficiency Bonus per Long Rest.

Claw Grip. You gain a Climb Speed equal to your Walk Speed.

Canis

You descend from a canine familiar lineage, such as a dog. As a Canis, you gain the following traits.

Guardian. You always stand alert. You add your proficiency bonus to Initiative checks.

Loyal. When you use the Help Action, the helped creature can add 1d4 to the d20 Check with which you are helping. You can use this feature as many times as your Proficiency Bonus until you take a Long Rest.

Corvus

You descend from a corvid familiar lineage, such as a raven. As a Corvus, you gain the following traits.

Mimicry. You can mimic simple sounds you have heard, such as a whisper or chitter. You must make a DC 10 Deception check for it to be credible, and the result of your check sets the difficulty for any Insight check made to discern the nature of the sound.

Sloppy Wings. Your heightened size makes it so you can't fly normally, but you can flap slightly. Have a Fly Speed equal to your Walk Speed, but if you are still mid at the end of a turn, you fall. You can ignore this restriction if another feature or effect gives you any flight speed.

Other

You descend from a different familiar lineage that doesn't fall under the most common categories. You gain Proficiency in 2 Skills or Tools of your choice.