If Po was in a bad mood 

Okay the Dead Po au is that Po dead when Lord Shen's canon hit Po he fell into the water, and died but his roll wasn't finished yet he went back and fought Shen then, when the battle was over Lord Shen escaped but before he left he grabbed Boss wolf however Po was aware of this so when Shen got away Po followed Shen and now Po just haunts Shen.