Valeant Pharmaceuticals, which has become the collective Achilles heel of a number of well-known hedge funds including Bill Ackman’s Pershing Square, has been crushed again. This time, the fall comes as the embattled company’s CEO returned from medical leave, canceled the release of quarterly earnings, withdrew forward guidance and disclosed an SEC investigation. All since Friday. As a result, the shares fell as much as 21% on Monday, closing at $65.80 apiece. The company, which traded for more than $260 per share in mid-August 2015, reached a 52-week low of $69.34 on November 18. “Valeant confirms that it has several...