Your Dexterity score increases by 2, and your Charisma score increases by 1.

Your Constitution and Strength scores decrease by 1.

Most cats live between 12 and 18 years.

Cats are typically a few inches under a foot in height, which climbs to about a foot and a half if they were for some reason standing on their hind legs. Your size is Tiny.

Your base walking speed is 40 feet.

You have a cat’s keen senses, especially in the dark. You can see in dim light within 60 feet of you as if it were bright light, and in darkness as if it were dim light. You can’t discern color in darkness, only shades of gray.

You have a climbing speed of 30 ft. and your claws deal slashing damage equal to 1d4 plus your STR modifier instead of the normal bludgeoning damage for an unarmed strike.

You have proficiency in the Acrobatics, Perception and Stealth skills.

You can jump up a number of feet equal to 5 plus your DEX modifier.

You take no fall damage from heights of 50 feet or less, and you take half damage from drops higher than that.

Assuming you're playing a cat that's granted the intelligence of a typical player character through some magical means, you can speak, read, and write Common and one other language of your choice.

Tiny Player Characters (5e Variant Rule)

The races presented in the Player's Handbook are all Small or Medium sized, and the weapons and combat rules presented therein are designed around those sizes. Until official Tiny player races come out, the following rules can be used to better represent them in combat.

Weapons

Tiny player races have special rules for weapons with the following properties:

• Tiny races do not benefit from the Light property, so these weapons cannot be used in the off-hand for two-weapon fighting. But they are still a one-handed weapon.
• Versatile weapons must be wielded in two hands, and deal their basic damage rather than their versatile damage.
• Tiny creatures have disadvantage on attack rolls with Two-handed weapons.
• Heavy weapons cannot be wielded by Tiny creature at all.
• All other one-handed weapons must be wielded in two hands.
• Tiny races do not benefit from the Finesse property, unless the weapon is also light.

To support Tiny PCs who wish to engage in two-weapon or ranged fighting, a new weapon property – Undersized – can be used. A list of undersized weapons can be found on the page linked.

Other Equipment

Other equipment typically work the same as normal when shrunk down to an appropriate size for the character. Tiny equipment will weigh 1/8 of medium counterparts and cost 1/4 when made by tiny crafters. Getting a larger creature to make tiny equipment normally costs the same as normal sized equipment due to the difficulty in crafting something so small.

Spacing and Movement

Although they cannot deal as much damage with weapons, Tiny creatures enjoy some benefits due to their size. As a Tiny race, you can:

• Squeeze into smaller spaces – as small as 15 inches
• Make better use of cover – in general, where another PC would gain half cover or three-quarters cover, you gain three-quarters cover and total cover respectively. You can also gain half cover from objects that would otherwise be considered incidental, such as rocks or tree saplings
• Occupy the same space as another Tiny or larger creature.

Encumbrance

Per PHB p.176, note that a Tiny creature's carrying and lifting capacity is half the normal for their Strength.

However:

• The DM may ask you to make Strength (Athletics) checks to move through terrain that other PCs would consider difficult terrain (such as travelling up stairs); and otherwise incidental terrain may be difficult terrain for you. A mount or larger PC could carry you!