**Core Concept**
Pemphigus is a group of autoimmune skin diseases characterized by intraepithelial blistering. The blisters form above the basal layer of the epidermis due to the breakdown of intercellular connections between keratinocytes.

**Why the Correct Answer is Right**
In pemphigus, autoantibodies target desmoglein proteins, which are essential for maintaining cell-to-cell adhesion in the epidermis. The formation of intraepithelial blisters occurs due to the loss of cell-to-cell adhesion, resulting in the separation of keratinocytes. This process leads to the formation of vesicles or bullae above the basal layer.

**Why Each Wrong Option is Incorrect**
**Option A:** Pemphigoid diseases, such as bullous pemphigoid, are characterized by subepidermal blistering, not intraepithelial.
**Option B:** Erythema multiforme is a skin condition characterized by target lesions, not intraepithelial blistering.
**Option C:** Stevens-Johnson syndrome is a severe skin and mucous membrane disorder, but it is not characterized by intraepithelial blistering.

**Clinical Pearl / High-Yield Fact**
Pemphigus is a classic example of an autoimmune disease that can be triggered by medications, such as penicillamine and captopril.

**Correct Answer:** C. Pemphigus.