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 onwards, Deerling can be bred in any form at any time if the parent is of that form.
Deerling is a fawn-like Pokémon, most resembling a fallow deer. The upper side of its body is pink in the spring, green in the summer, orange in the autumn, and brown in the winter. It has a yellow patterned rim, and its underside is peach. It sports a yellow floral tuft on its head, 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. It can change in appearance with the changing of the seasons. If it senses animosity, it hides in tall grass. It moves in herds as it is timid around humans. It dwells in sparsely populated areas, away from humans. It is herbivorous.
A herd of Spring Form Deerling appeared in In The Shadow of Zekrom!. Another herd appeared in Enter Iris and Axew!, where Ash attempted to catch one; however, as he had not weakened it, the Deerling was able to deflect the Poké Ball and fled with the rest of the herd.
A wild Spring Form Deerling appeared in Sewaddle and Burgh in Pinwheel Forest!. A Sewaddle accidentally latched onto it with String Shot, startling the Deerling. This caused it to buck and thrash around wildly through the forest in an effort to get Sewaddle off, but this put Sewaddle in serious danger.
Ash saved two Deerling from falling off a cliff at the beginning of White—Victini and Zekrom and Black—Victini and Reshiram. In Victini and Zekrom, the Deerling were in their Autumn Form, while in Victini and Reshiram, they were in their Summer Form and Autumn Form.
An Autumn Form Deerling appeared in the opening sequences of White—Victini and Zekrom and Black—Victini and Reshiram, while multiple Summer Form Deerling appeared in both movies proper. Two Summer Form Deerling were saved by Ash and Victini when they were in danger of falling off a cliff face.
Multiple Summer Form Deerling physically appeared in Kyurem VS. The Sword of Justice. Multiple Deerling also appeared in their Spring, Summer, and Autumn Forms during the Swords of Justice legend.
Multiple Summer Form Deerling appeared in Genesect and the Legend Awakened, where they were among the many Pokémon residing at Pokémon Hills. Two of them later helped put a fire out there.
Darlene, a female Deerling, was captured by White during her preparation for the Battle Subway trial in Growing Pains. She was seen in her Summer, Autumn and Winter Forms.
Deerling may be a combination of deer and yearling (referring to both its young age and its ties to the year's four seasons) or sapling (referring to its Grass-type and abilities). Alternatively, it may be a combination of dear and darling, both common terms of endearment.
Shikijika is a combination of 四季 shiki (four seasons) and 鹿 shika (deer).