In Episode 12 of Grimm Season 6, "Zerstorer Shrugged," Zerstorer walked in through the mirror to arrive in Portland with his staff. He did not waste much time to begin his game of death and destruction. The closing moments saw the devil killing Wu (Reggie Lee) and Hank (Russell Hornsby) using his staff.
And it looks like Hank and Wu might never wake up. In a sneak peek released for the final episode, "The End," Nick can be seen unable to resurrect them using the stick, which might be the final piece that Zerstorer needs to get his staff to full power.
In a second sneak peek, he is seen telling Trubel (Jacqueline Toboni) that Hank and Wu are dead, adding that the stick is not working. He is unable to understand why Zerstorer did not kill him, although he killed everybody inside the precinct.
It might be because he wants the stick, as in one sneak peek, Diana is seen informing Nick and the gang that the stick tells Zerstorer all about him and his location, adding the devil wants the stick. The clip ends with the cabin door opening and Zerstorer walking inside with his staff. The power that the staff releases brings down all the men and women except Diana, who can be seen facing him with her eyes turning purple.
If not stopped, the invincible Zerstorer is capable of triggering apocalyptic events that may precipitate the end of the world. Moreover, Grimm Season 6 Episode 13 synopsis states that Nick must seek his ancestors' strength to save the world from a terrifying end.
The synopsis also says that a rare potion may help the fight.
"Nick faces off against his greatest foe yet as it seems no weapon can defeat him. At the Spice Shop, Monroe, Rosalee and Eve search for answers and stumble upon a rare potion that may help the fight. Elsewhere, Capt. Renard and Adalind try to keep Diana and baby Kelly safe as the threat has its eyes set on the children."
Monroe is seen saying, "when the beast appears invincible and death the only fate to those who fight it, only the strength of one's blood can overcome the great evil and destroy the destroyer."
Rosalee seems to know about the potion, which is made using the blood of three opposing forces -- a Grimm, a Hexenbiest, and a Wesen. The clip ends with Monroe saying, "Dude, we're taking you down."