Question: When Mantis keeps the wolf from firing the weapon, he shouts, "Fear the bug!" Is it some kind of a parody?
Chosen answer: No, it is merely a joke about the size of Mantis and his surprising fighting prowess. "Fear the..." is a somewhat common joke. For example, the University of Maryland uses the unofficial slogan "Fear the turtle!"; the Milwaukee Bucks use the slogan "Fear the deer", etc.
Question: How did the soothsayer survive the collapse of the tower?
Answer: More than likely she wasn't in the tower when it was destroyed. She directly confronts Shen about destroying the tower and makes no mention of having survived it's collapse. She only comments on his recklessness in destroying his ancestral home.
Answer: Since Po's father was presumably the only panda to attack Shen's wolves head-on, there's a chance Shen could have seen him. Plus in the flashback, Shen orders his wolves to attack Po and his mother before Po's father defends them both with his mallet.