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.
Deerling is a deer or fawn-like Pokémon, most resembling a fallow deer. The upper side of its body is colored either pink, green, orange, or brown—depending on the season—and is rimmed and dappled with yellow patterns, with the underside of its body being a lighter beige shade. It sports a yellowish-colored, floral tuft on its head, and similar yellow coloration on the ear insides of its tapering ears. The tips of its limbs are colored black and its pink tail is small. Despite this, Deerling changes in appearance with the changing of the seasons: in the spring it is pink, in the summer it is green, in the fall it is orange, and in the winter it is brown.
Deerling can be found almost anywhere throughout the Unova region. It seems as if this Pokémon can adapt according to the season and temperature, and this is why there is a laboratory in Unova designated to the studies of the powerful ability of adaptation that Deerling and their evolved form possess. This Pokémon dwells in sparsely populated areas, away from humans. The tend to hide in tall grass when they sense animosity. Deerling tend to move in herds due to their timidity towards humans.