Chub is a large, pale yellow-colored maggot with two segmented body and beady eyes. Her mouth appears to be smaller, but when she charges at Isaac, her mouth becomes very huge when opening her mouth wide. In addition to her mouth while performing a charge attack, it is filled with large teeth.
Chub charges at Isaac quickly while opening her mouth wide when he gets in her line of sight. However, Isaac usually has enough time to sidestep away. Dropping a Bomb in the path of her charge will cause her to eat it. This stuns her for a short time, and then explodes inside her, dealing a large amount of damage.
Chub can also spawn Chargers, up to a maximum of two at once. These Chargers can be destroyed by her own charge if they get in her way.
Unlike most attacks early in the game, Chub's charge will deal a full heart of damage if it hits instead of half a heart.
From the Afterbirth expansion for Rebirth, in the Flooded Caves level, she can spawn a Drowned Charger.
She is much larger in size, much more resistant to knockback, and slow. Instead of spawning chargers, she'll spawn blue Boils (functions identically to regular Boils, and does not drop any Pick Ups upon death).
She is slightly smaller than normal, and she has much faster and more unpredictable movement, both when moving normally and charging at Isaac. She will spawn Spities instead of Chargers, up to a maximum of 2.
Outside of Boss rooms, Chub may occasionally spawn without her 3rd segment making her unable to spawn enemies. In this form, Chub may use the spawning animation, but will not spawn any enemies in this situation, leaving her briefly vulnerable. Typically spawns with two Larry Jr. bosses with her. This is an intentional weakening of the boss, possibly for balance reasons.
Eternal Chub acts the same as normal one, but she always spawns 2 Chargers and some of them will be their Eternal variants.
From one of the sketches of the artbook, Chub suppose to swell her cheeks after swallowing a bomb.
Her alternate name "Mrs. Maggot" from the artbook turns out to be misspelled as "Mr. Maggot".
Chub's tendency to eat bombs only to have them blow up internally is very reminiscent of the Dodongos and Dodongo Snakes from the Zelda series.
Chub's face in the title card from the original The Binding of Isaac game is almost exactly like the one shown in the "Poker Face" meme. This is very likely intentional.
Chub has been identified as female via Edmund's formspring account .
During her death animation, Chub is bursting tears of blood. That also goes to her posthumous counterpart Carrion Queen.
From the original game, the way how she opens her mouth while spawning Chargers is much wider that in Rebirth.
When using Mom's Pad against Chub, her segmented body will split apart (as shown from the image of the right).
If fighting her as a mini-boss, where the doors or a secret room entrance is bombable, it is possible to win against her incredibly easily if Isaac has two bombs. Bomb one of the doors, and make her charge into it. She will become stuck in the door, allowing Isaac to freely damage her. However, she seems to not take damage from tears and has to be finished off with a second bomb. Also, if Isaac has XRay Vision, he doesn't need to spend any bombs to trap her in the door.