**Core Concept**
Pemphigus vulgaris is an autoimmune disease characterized by the formation of flaccid bullae due to the breakdown of intercellular connections between epithelial cells. It is mediated by autoantibodies against desmoglein 3 proteins, which are crucial for maintaining cell-to-cell adhesion.

**Why the Correct Answer is Right**
The autoantibodies in pemphigus vulgaris bind to the extracellular domain of desmoglein 3, disrupting the cell-to-cell adhesion and leading to the formation of flaccid bullae. The disease can also involve the oral mucosa, resulting in mucosal lesions. The pathogenesis involves the activation of complement and the recruitment of neutrophils, which further exacerbate the tissue damage.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because Stevens-Johnson syndrome is a drug reaction or infection-induced condition characterized by skin and mucous membrane lesions, but it typically presents with erythematous rather than flaccid bullae.

**Option B:** This option is incorrect because epidermolysis bullosa is a group of genetic disorders that result in blister formation due to mechanical trauma, but it is not typically associated with oral mucosal lesions.

**Option C:** This option is incorrect because dermatitis herpetiformis is a chronic skin condition characterized by intensely itchy, blistering skin lesions, but it is not typically associated with oral mucosal lesions.

**Clinical Pearl / High-Yield Fact**
Pemphigus vulgaris is often associated with other autoimmune diseases, such as lupus erythematosus, and can be triggered by certain medications, such as penicillamine and captopril.

**Correct Answer:** C. Pemphigus vulgaris.