Deerling changes its appearance depending on the current season. However, this change in form does not occur after capture, unless it is present in the player's party at the time of a season change. This applies to Eggs as well.
When the month is January, May, or September, the season is Spring, and it becomes Spring Form.
When the month is February, June, or October, the season is Summer, and it becomes Summer Form.
When the month is March, July, or November, the season is Autumn, and it becomes Autumn Form.
When the month is April, August, or December, the season is Winter, and it becomes Winter Form.
From Generation VI to VIII, seasons are not a mechanic, and only the Spring Form is obtainable in the wild. However, its other forms are retained upon transfer from Generation V and can be passed down via breeding.
In Pokémon Scarlet and Violet, Deerling's ability to change forms returns, and is done through the same method as in Black, White, Black 2, and White 2. However, the form it will become is now based on the location that the game is loaded in. In general, Spring Form Deerling are located in the South Province (Areas One, Two, Three, Four, and Five), Summer Form Deerling in the East Province (Areas One and Two), Autumn Form Deerling in the West Province (Areas Two and Three), and Winter Form Deerling in the North Province (Dalizapa Passage and Glaseado Mountain).
Deerling is a Pokémon that resembles a deer fawn. The upper side of its body is pink in the spring, green in the summer, orange in the autumn, and brown in the winter. Deerling has a yellow-patterned rim, and its underside is peach. It sports a yellow floral tuft on its head with small antlers hidden underneath, and similar yellow coloration on the insides of its tapering ears. The tips of its limbs are colored black and its pink tail is small. Deerling also has a different scent depending on the season. In spring, its scent is delicate, sweet, and calming. In summer, it has a distinct grassy scent. In autumn, it has a softly sweet scent. And in winter, Deerling has no scent.
If Deerling senses animosity, it will hide in tall grass. It moves in herds, as it is timid around humans. Despite this, Deerling does whatever it wants, even around humans. Deerling will take a liking towards anyone who feeds it. It will playfully headbutt anyone it likes, even if headbutts are a little painful. It dwells in sparsely populated areas, away from humans. It is herbivorous. Despite their innocent and adorable appearance, Deerling are considered pests by farmers, as they tend to eat all of their plant shoots. Lycanroc is a natural enemy of Deerling; farmers often use Lycanroc to guard their fields from Deerling.
Deerling's Autumn Form has, to date, only ever been released as a Pokémon card once; because this card was never released outside of Japan, Autumn Form Deerling has never appeared in the International Pokémon Trading Card Game.
Deerling's Winter Form is its only form that has not appeared in the anime yet.
The colors of its four different seasonal forms may be visual references to the colors of trees and bushes during the four seasons: with pink representing blossoms in the spring, green representing fully grown leaves in the summer, orange representing the changing leaves in the autumn, and brown representing the bare, leafless tree and bush branches in the winter. Deerling's design was worked backwards from Sawsbuck's design.
Deerling may be a combination of deer and darling or yearling (young animal between the age of one to two years old), with -ling being a common suffix to denote something that is small or immature.
Shikijika may be a combination of 四季 shiki (four seasons) and 鹿 shika (deer).