Tessa

Tessa is...

insatiably curious, daring, and a bit rambunctious, Tessa is known for her mild obsession with horses, her fascination with all things in the sky, and her propensity for needing a lot bandaids. She is a skilled ballerina and quite proud of her space unicorn Lisa Frank trapper keeper. Canonically, she is the oldest of the children, being just over 12 years old.

Biography
Initially homesick for her twin brother, Bradley, part of Tessa's early character arc involves her developing her own sense of self separate from just being one of "the Twins" (though Bradley  would subsequently appear as a guest character in seasons 2 and 3). She also has a penpal, Alex, that she writes to frequently; Alex was first shown on screen in the season 3 episode "I Dream of Alex", after Tessa cast a spell that allowed them to share dreams together in order to help Alex overcome a recurring nightmare.

She dreams of being a scientist when she grows up, and her enthusiasm for nature, space, and unsolved mysteries reflect this. However, she's just as keen on witchcraft as the other children at camp, and is often seen trying to tackle advanced spells, often with mildly explosive results (frequently followed by her catchphrase "Oh, that was awesome!").

Tessa is known for accumulating mild injuries over the course of an episode- however, rather than crying and being upset, she typically shrugs them off and keeps going

Behind the scenes
The running joke about Tessa being able to draw anything, as long as it's a horse, is based on a true story- horses really are the only thing show co-creator Theresa Fisher knew how to draw as child.

Her penpal relationship with Alex was added to give her character an additional avenue for narration. Amongst the Camp Discourse fan community, Alex and Tessa are a frequent target for shipping, and are referred to collectively as Tesex or Alessa. The heart-framed picture of them seen briefly in the background during the Camp Discourse movie Next Summer has been confirmed by Theresa Fisher as a subtle nod to this pairing.