**Core Concept**
The question is testing the student's knowledge of cardiotoxic drugs, which are substances that can damage the heart muscle or disrupt cardiac function. Cardiotoxicity can occur through various mechanisms, including direct damage to cardiac cells, disruption of ion channels, or interference with the heart's electrical conduction system.

**Why the Correct Answer is Right**
The correct answer, **Digoxin**, is a cardiotoxic drug that can cause digitalis toxicity. Digitalis toxicity occurs when the drug accumulates to toxic levels, leading to an increase in cardiac contractility and a decrease in the heart rate. This can result in arrhythmias, such as atrial fibrillation with rapid ventricular response, and can even lead to cardiac arrest. Digoxin inhibits the sodium-potassium ATPase pump, leading to an increase in intracellular calcium and an increase in cardiac contractility.

**Why Each Wrong Option is Incorrect**
* **Option A:** **Lidocaine** is a local anesthetic and antiarrhythmic medication that is actually used to treat certain types of arrhythmias, rather than causing them.
* **Option B:** **Magnesium** is an electrolyte that is essential for cardiac function, and magnesium deficiency can actually increase the risk of arrhythmias.
* **Option C:** **Quinidine** is another antiarrhythmic medication that is used to treat certain types of arrhythmias, rather than causing them.

**Clinical Pearl / High-Yield Fact**
To remember the signs of digitalis toxicity, the classic mnemonic is "A, B, C, D, E, F": Arrhythmias, Bradycardia, Conduction block, Decreased contractility, ECG changes, and Fatigue.

**Correct Answer:** D. Digoxin.