You have proficiency in picking locks due to the dexterous nature of the grimalkin and their fascination with puzzles and problem solving. Add your proficiency mod to any checks you make trying to pick a lock

You can see in the dark like it is lit out to 60 feet in shades of gray

You are able to cast detect invisibility and invisibility once before needing to take a long rest. You also gain the ability to launch furballs through an intense bit of regurgitation

Estray:

A grimalkin in this phase wears clothing, speaks, and walks upright. It is, by all appearances, a humanoid cat, with fur covering its little body (they are 4’ at the very tallest). Sometimes friendly with mortals, sometimes tricksome and perilous, the grimalkin in estray is generally tolerated in most towns and villages, provided it behaves itself. the racial feats listed on the grimalkin apply to the estray

Chester:

In chester, a grimalkin resembles a normal cat in all respects—though it is perhaps unusually fat in comparison to the average mouser. A grimalkin in chester retains a dull-witted intelligence (INT score halved) and can understand language, but can only respond in yowls and meows. Being in chester is especially embarrassing to a grimalkin and something it will usually seek to avoid. It cannot cast spells in this phase and, self-evidently, no longer has the physiology to wield weapons or pick locks. Abilities in Chester Combat: The grimalkin may make a claw/ claw/bite attack routine each round, with each hit inflicting 1 point of damage.

Transformations To estray: At dawn, the grimalkin returns to its estray form, unless it wishes to remain in chester (in which case, it may transform back to estray at any time). Spells of alteration may also be cast upon it to initiate the grimalkin’s transition back to estray-form.

Wilder:

A grimalkin in its primal fey form is difficult to see clearly in the mortal world as more than a gleaming pair of deranged, predatory eyes. Those who can see in darkness or perceive the invisible discern a bulky, feline form, 3’ high at the shoulder, with an abnormally large head, a leering mouth, and fur standing on end, as if electrified. In the mortal world, this phase is very unstable. 

Combat: While the wilder-grimalkin is cunning and clever, it does not have the sense to wield tools or weapons. However, the grimalkin may make a claw/claw/bite attack routine for 1d6/1d6/1d6 damage. These attacks count as +1 magical weapons.

Primal strength: While in wilder, the grimalkin gains 2d6+2 temp hp and loses it when transformed back into estray

Veiled in darkness: The wilder-grimalkin is only semi-visible, incurring a disadvantage penalty to attacks against it by those who cannot see invisible / in darkness.

Weaknesses in Wilder

Creature of shadows: Contact with even a sliver of the sun’s rays will transform the widler grimalkin into knotty hardwood. (A save vs petrification is allowed, per round of exposure.)

Fey chaos: Being in this phase suppresses a grimalkin’s memories and it cannot distinguish friend from foe. When it transforms to this phase during battle, the grimalkin will indiscriminately attack all nearby living creatures until the combat comes to an end. At this point, it will disappear into Fairy, coming under the referee’s control.

Transformations (Wilder) To estray: After a certain period of time (determined by the referee), the grimalkin spontaneously reverts to estray, having wandered strange paths in Fairy for some time

In combat with large or biggercreatures, the estray grimalkin gains a +2 bonus to Armour Class, due to its small size

Being of the feline and fey type, you have a unique charm about you and your reflexes are honed to the razer's edge