**Core Concept**
Malignant hyperthermia (MH) is a life-threatening medical emergency triggered by certain volatile anesthetics and depolarizing muscle relaxants. It is characterized by a hypermetabolic state, muscle rigidity, and subsequent heat production, leading to hyperthermia.

**Why the Correct Answer is Right**
The correct answer is not provided, but based on the options typically seen in MH, we can infer the correct answer. MH is typically characterized by muscle rigidity, high metabolic rate, hyperthermia, tachycardia, and increased end-tidal CO2. These symptoms are a result of the sustained depolarization of skeletal muscle cells, which leads to an uncontrolled release of calcium ions from the sarcoplasmic reticulum.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is often seen in MH, as patients typically exhibit muscle rigidity, which is a hallmark of the condition. Muscle rigidity is caused by the sustained depolarization of skeletal muscle cells, leading to an uncontrolled release of calcium ions from the sarcoplasmic reticulum.

**Option B:** This option is also seen in MH, as patients often exhibit tachycardia, which is a result of the hypermetabolic state and subsequent increase in catecholamine release.

**Option C:** This option is not typically seen in MH, as patients do not exhibit a decrease in end-tidal CO2. Instead, end-tidal CO2 levels are often elevated due to the increased metabolic rate and subsequent increase in carbon dioxide production.

**Clinical Pearl / High-Yield Fact**
A key clinical feature of MH is the rapid increase in end-tidal CO2, which can be used as an early indicator of the condition. This is because the increased metabolic rate leads to an increase in carbon dioxide production, which is reflected in the end-tidal CO2 levels.

**Correct Answer:** C.