Perrigo (PRGO) is now Hayman Capital's second-largest equity position.

Perrigo makes store-brand OTC products and generic prescriptions. It also makes store-brand infant formula.

This is significant because Bass has been at war with the US pharmaceutical industry since the beginning of the year.

So far in 2015 he has filed 13 inter partes review (IPR) petitions with the US Patent and Trademark Office challenging the patents of six publicly traded pharma companies.

It's part of a new "short activist strategy" where Bass writes an IPR challenging the validity of a patent, while also shorting the company's stock.