Okay, this is a jumping off point for myGrimm/Mass Effect Crossover Challenge. Nobody has to use this piece. It's just meant to act a helpful starting point. It's kind of what I had in mind.

Challenge #1:

The Grimm Effect

The Shadow Broker turned to face Liara, although his—its?—face remained hidden by the shadows. "It's pointless to challenge me, Asari. I know your every secret, while you fumble in the dark. For instance," the hulking alien said turning to view the group as a whole. "I know your beloved Commander has been keeping some very . . . interesting secrets from you."

Shepard felt a chill run through her veins in spite of the burning atmosphere outside the shuttle. Her rifle wavered just a little before she forced it steady. Could he know? Of course not; it was impossible.

"Tell me, Commander, when were you planning to tell your lover that you were a Grimm?"

Shepard's heart stopped. He knew. She swallowed, trying to organize her thoughts.

"Surprised, Commander?" the Broker asked. "Do not be. I have spies from every race in the galaxy, including wesen. I could recite every member of family to bear the "gift" all the way back to Nicholas Burkhart, even his aunt and mother. I can identify at what age you awakened to your heritage and summarize most if not all of your hunts. I am also well aware of your allies: the Blutbad Lieutenant Williams, the Hexenbiest Lawson, the Hundjaeger Taylor . . . Quite the company you keep."

"Shepard . . ." Garrus asked. "What's he talking about?"

"I'll tell you later," the Specter replied, trying to recover. How was she supposed to explain this—that she could see . . . creatures that normal people couldn't? It sounded more like insanity than some kind of family trait.

"Shepard . . ." Liara whispered, turning just slightly to look at her lover. She didn't say a word, but her eyes carried a look that hurt the Commander worse than any bullet wound. A look of . . . betrayal.

"I promise, I'll explain everything to you, Liara, but you'll have to wait until we deal with this guy."

"Arrogant," the Shadow Broker declared, leaning over his desk as though he were a critic at a play. "You really believe you can kill me?"

"I'm a Grimm, remember?" Shepard countered. "Monsters flee in terror at the sight of me." She would have to figure out a way to deal this revelation later—Thane, Tali, and everyone else would have to know, too, now-and she'd have to pull off the minor miracle to save her relationship with Liara. But, right now, there was a bad guy to fight, and she had a gun: life at its most basic.

O.K., time for a reiteration of the rules.

1. Shepard must a descendent of Nick. This also extends to her style of dealing with wesen; she's not the type of Grimm who'll lop off the head of a wesen the instant she sees it.

2. Cerberus is a descendant of the Verrat. The Illusive Man is a Royal. Personally, I don't think they're very special anymore, because Nick, Renard, and company, but it's up to the writer.

3. Not every human in the crew needs to be wesen. It would work pretty well if only a few were.

4. The key should be involved. I don't know or care how, but it should be.

5. You don't necessarily need to keep it limited to canon wesen. If someone wants to include some of the monsters from Supernatural (like vampires, djinn, or sirens), that would be great. Just don't include anything too overpowered-going back to Supernatural, no angels or demons, those guys are way too much (personally, I don't care much for them, anyway).

6. Remember, Grimm is primarily a show about mystery. Action and adventure is good, great even, but don't just through creatures at the crew for them to shoot at. Make it interesting, a Ziegevolk influencing a court case, a Hundjaeger assassin hunting down a target, Hasslichen extorting a lodge of Eisbiebers, you know the drill.