Critters will make noises when hungry, but won't die if not fed (note: critters rather 'spoil' than 'get hungry'). Critters can be fed anything edible, including Eternal Fruitcake, Rot, and Rotten Eggs. Every food given refreshes critter spoilage time to its maximum. Critters have spoilage time (will be starving) of 2 days. Time is affected by weather the same way other perishable items are.
There is a "mini-game" around the maximum spoilage time. Player can increase this time to up to 4.5 days (5.5 for "Plump" critters) in the increments of 0.5, by feeding it when it is between its 20% and 50% freshness. When it is fed when below 20% freshness, this time will decrease. Feeding it when above 50% freshness have no effect on the maximum spoilage time. A Critter can be "pet" by clicking on it, triggering a small animation.
Each player can only have one Critter at any given time. To get a different Critter, players must "Abandon" their current one by being near the Rock Den and right-clicking that Critter. Walter's Woby counts as pet, making Walter unable to adopt critters from the Rock Den.
A Mothling is a juvenile version of a Moon Moth. Mothlings can be obtained in exchange for a Moon Moth and Flower Salad. Unlike other critters, which have no function, Mothlings can act as a light source. A Mothling will not give off light when hungry.
Critters can have traits which determine their behavior. Player actions add or subtract points from one of the Critter's traits, depending on the action, with the trait having the most points becoming the dominant trait and an adjective is shown in the Critter's name.
A Critter's first dominant trait is determined after 10 days of obtaining the Critter, and dominant traits are reassigned every 1.75 to 2.25 days.
Trait points decay at the rate of 0.7 point per day for playful and well-fed, 0.9 points per day for crafty and 1.35 per day for scrappy trait. The maximum amount of points a Critter's trait can have is 40, while the minimum is -6. Should all traits on a Critter have a negative point value, the Critter will revert to having no traits, and the next dominant trait is assigned after 3.75 to 4.25 days.
Performing an action that adds points to a trait that is already the dominant trait gives a 10% bonus to the points added to that trait.
The current dominant trait can be locked in permanently by feeding the critter any "goodie" food - this includes Taffy, Jellybeans, Mad Science Lab potions, and Winter's Feast candies. After that, the trait will never change until player abandons the critter.
The Scrappy trait is given to Critters when the player fights or kills Monsters. Killing small and passive Animals such as Rabbits doesn't count towards this trait.
The Combat trait adds the adjective "Scrappy" to the Critter's name and makes them perform aggressive animations towards monsters (but does not make them able to fight).
The Crafty trait is given to Critters when the player Crafts items and Structures excluding Walls.
The Crafty trait adds the adjective "Crafty" to the Critter's name and makes them perform a special animation when the character is doing work (chopping, mining, digging), or crafting.
The Playful trait is given to Critters when the player pets them and when they play (either by themselves or with other players' Critters). Bonus points are awarded when the player pets critter after it nuzzles.
The Playful trait adds the adjective "Peppy" to the Critter, increases the range at which they play with other Critters, and makes them play more often (effectively decreasing the rate of point decay, since playing adds points to this trait).
The Well-fed trait is given to Critters when the player feeds them. All Crock Pot dishes give 4 points, while other edible items gives 1 point. The Critter's favorite food is the food item used in order to adopt it, and feeding a Critter its favorite food gives 5 points to this trait. The points added to the trait are affected by the Food's freshness and its type and if it's the Critter's favorite food. Fresh food gives the full value, Stale food gives half (50%) of the value, and Spoiled food gives only a tenth (10%) of the value.
The Well-fed trait adds the adjective "Plump" to the Critter's name and increases the spoilage time to 3.25 days. This spoilage time can be increased to up to 5.5 days. No matter at which phase of "Plump" critter's freshness it is fed, its spoilage time will never go below 3.25 days.
The Kittykit's name seems to be a mash up of the name for baby cats and baby racoons, "kitten" and "kit", as well as a play on the term "kitty cat".
It used to be called the Kittycoon.
Despite their name, the Vargling's appearance is more similar to the Hound. Furthermore, Wigfrid refers to it as a hound and they are made using Hound's Teeth.
Wickerbottom refers to the Vargling as Canis lupus which is the scientific name commonly referring to the Gray Wolf. Suggesting that the Vargling, and to an extent the Hounds and Varg, are related to said wolf.
The two skins added for the Vargling during the Chinese New Year event Year of the Varg, alludes to two dog breeds that supposedly originated in China; the Chow Chow and the Shih Tzu.
There is an extra function in the Critters code called "IsSuperCute", which does nothing except return "true".
Strangely, feeding a critter Rot or Rotten Eggs stops its hunger cries, despite them making players lose hunger points.
The Vargling, Kittykit, and Ewelet as they appear in the Cute Fuzzy Animals update poster.
The Broodling and Glomglom as seen in the Herd Mentality update poster.
The Kittykit and Broodling as seen in the Winter's Feast update poster.
The Critters (minus the Giblet and Mothling) in the A New Reign: Part 2 trailer.
A Kittykit and WX-78 running from a cave-in as seen in the A New Reign trailer.
A drawing of Willow, Wendy, Maxwell, and Wilson with their critters (the Broodling, Vargling, Glomglom, and Kittykit, respectively) from Rhymes With Play.
Concept art for the Giblet.
The Giblet as seen in a drawing from Rhymes With Play.
A Vargling as seen in a promotional image for Rhymes with Play # 172.
An animated sequence of a Vargling chasing a ball from Rhymes with Play # 172.
A drawing of all Critters except the Kittykit from Art Stream # 4.
Glomglom with Glommer on the 2017 Valentine's Day Cards.