A bit more of a comedic/dramatic Halloween idea... Jaune transforms into a human/Grimm hybrid with enhanced strength, speed, tentacles, etc. He has no idea how, or why.
It turns out that Nick Arc is in fact the son of Oz and Salem (They hooked up a few years back, as they still do because their relationship is so toxic it makes Chernobyl look like Three Mile Island). This explains why Nick is so insanely durable and why he never discovered his Semblance: His Grimm side combined with his powerful Aura made him a human tank. So he didn't need to find out.
This of course is rather concerning. Ironwood wants to take the whole Arc Clan into custody, Ozpin is against it as Nick and his children are his family, and Salem is shocked that her child actually is a perfect fusion of human and Grimm-Previous times this happened, the child was pure human and she just dropped them in orphanages to keep them away from her.
Jaune himself and his friends no doubt have some... Thoughts.
Blake: "T-Tentacles..."
Pyrrha: "Tentacles?"
Yang: "Tentacles~..."
Jaune: "Guys? Can we focus?!"
And with his parents...
Jaune: "MOM! Did you know?!"
Isabel: "Of course I knew! Your father told and showed me before we got married! I was scared at first but he told me he had no idea why he was this way! I've studied him and all of you for years but none of you showed any signs of Grimm hybridization until now! Not even Tangy and she's bloodthirsty!"
With Nick and Ozpin...
Ozpin: "I'm sorry I didn't tell you sooner, Nick. I'm sorry I lied. I'm sorry you had to suffer that orphanage, growing up alone... I have made more mistakes than any other man... But these are the worst ones I have made. I won't ask your forgiveness-"
Nick: "But I do forgive you, Dad!"
Ozpin: "What?"
Nick: "Look, maybe I'm dumb but I'm not that dumb. I get it. And while my life was hard, it taught me what really mattered: Love, family, friendship. And you have a very heavy burden, Dad. I understand that... And while I'm not happy I had to go through all that, I am happy you didn't abandon me because you hated me or discarded me, you just didn't know. And you're very sad because of the right reasons. That means you're a good man, who had to make terrible decisions... And I can forgive that."
Ozpin: Holds back tears "... I do not deserve a son like you..."
And with Salem...
Salem: "Wait... This means... GRANDBABIES!"