Anxiety

is an emotion that while the old emotions were controling Riley's emotions in Riley's mind, Anxiety touched with his/her finger on the button to make Riley feel an Anxiety emotion. Once every emotion backed away from Anxiety suprised that there's an new emotion wich it appears to be an Anxiety.

Anxiety knows about Riley's control panel where Anxiety can make Riley feel Anxiety while Anxiety emotion is touching the sore of button on the Riley's mind panel inside of her head.

appeared as an orange emotion with her weird-anxiety hairstyle of the same color and jade green eyes, orange and white-striped long-sleeved shirt, brown pants attached by a black belt with a gold buckle, and brown shoes.

Like its namesake,
Like its namesake, Anxiety is shown to be a nervous emotion with some luggage to get off (and that’s no figure-of-speech, because she was carrying some suitcases when she meets the emotions). She's extremely anxious about meeting preexisting emotions like Joy, especially because she wants to make a good first impression.

Anxiety is the very first emotion to be formed in Riley's mind ever since her toddler years, being also the very first emotion to be introduced at the beginning of Riley's adolescence.
She is also the fourth female emotion to inhabit Riley's mind.
Her sudden appearance on HQ and before the other new emotions may be a reference to her eagerness to start her new job and meet her new colleagues, which is a characteristic of the emotion she embodies. Anxiety also knows the first emotions that came to Riley's mind are, Joy, Sad, Fear, Anger, Disqust.
Once Anxiety entered the Riley's mind Anxiety pressed the button on the control panel inside of Riley's mind to control her emotions.
She is the only new emotion who's eyes don't match her body. The way the other emotions met Anxiety is similar to how Joy met Sadness, since they only noticed her when the console turned orange, Anxiety's color. The same thing happened when Joy met Sadness, where the former only noticed the latter when she made Riley cry when she turned the console blue. Anxiety is showed to be a heavy packer, since she possess a lot of baggage to unpack now that she had settled on HQ.+

+This can be seen as a reference to her own emotion, since people who possess a lot of negative experiences and disappointments that affect their own behavior and/or interactions with other people are said to "have a lot of baggage". This can also represent Anxiety's very need to be always prepared for anything and try to control any problem that may arise before they are even a reality, which contrasts with the core emotions who normally react to the problems and deal with them as they come. She’s sort of the odd-name-out with the new emotion characters because she’s the only one of them who’s name doesn’t start with an ‘E’.
Based on how she said ‘we’ (referring to the other new emotions that appear in the sequel) after meeting with the old emotions, it’s likely that she (and by extension the other new emotions) already existed within Riley’s mind since the first movie.

Joy: she is an emotion with a somewhat human appearance, although she doesn't have toes. She has a knee-length green dress with no sleeves. She has very short hair as if she were a boy and it's blue in color. Her eyes are sky blue and she shines, her light is blue. She is the leader of the emotions. She shows no interest in boys. She is a tall girl. His skin is yellow

Sadness: she is the same size as Anxiety, so she is somewhat small. Compared to Joy, Sadness is smaller, it reaches up to Joy's chest. Sadness is wearing a white turtleneck and blue jeans with blue slippers. She has round glasses and her hair is blue with short hair and her skin is sky blue. She is always sad and discouraged all the time, being pessimistic. Blue eyes

Anger: he is a small boy who has no hair. He is a bit square and his skin is red. His clothes are a white shirt with a red tie, black pants, and black shoes with a brown belt. When he gets angry, fire comes out of his head, that's why he's bald. He's always angry or his attitude is as if he were angry. Red eyes

Fear: he is a tall and slim boy with purple skin, his eyes are light purple. His clothes are a white shirt with black pants. He is always scared and cautious about things that happen. He has a little hair, with some long hairs.

Disgust: she is a girl with light green skin, green eyes, short but cute dark green hair. She is always fashionable and likes everyone to look good. She has a dark green dress with a fuchsia scarf around her neck and dark green heels.

Envy: she is very small, a small emotion which has dark turquoise hair that is short and wavy, her skin is turquoise. Big and beautiful eyes which shine with the desire to possess something. She has the appearance of a little girl who wants everything she sees. She is a good friend of Anxiety. Her outfit is a little light purple dress with white dots, along with dark turquoise pants and fuchsia shoes. She admires Disgust for how good she looks.

Embarrassment: he is a tall and robust boy, his skin is light pink and his hair is an intense pink color. He always has a white jacket which he uses to cover his face when he is embarrassed along with some black pants.

Ennui: is a tall and thin girl with a French accent, her name means "boredom". She has long hair with bangs. Her hair is dark purple-blue and her skin is light purple-blue. Her clothes are a dark blue shirt with dark blue pants. She is always bored and always with her cell phone.

These emotions were the ones that came along with Anxiety