Warning: SPOILERS Below for Happy Death Day 2U:

Happy Death Day 2U ends with a post-credits scene that sets up Happy Death Day 3. The stinger also opens up the world of Happy Death Day beyond the college campus of Bayfield University and hints at the greater ramifications of the technology that caused the time loops that trapped Tree Gelbman (Jessica Rothe).

The big revelation in Happy Death Day 2U was that Tree's time loops were caused by a device invented by Ryan (Phi Vu), the geeky roommate of her boyfriend Carter (Israel Broussard). Ryan and his lab partners Samar (Suraj Sharma) and Dre (Sarah Yarkin) built a machine called the Sisyphus Quantum Cooling Reactor (SISSY for short), which they hoped would prove time could be slowed down. Instead, SISSY malfunctioned and caused Tree to get caught in a time loop in Happy Death Day. When Tree finally freed herself, the loop ended up being passed to Ryan, who found himself the victim of his own Babyface Killer. Happy Death Day 2U gets even weirder, with Tree ending up not just in a new time loop but also trapped in a parallel dimension - which she prefered for a while since it mostly seemed like a better version of her life.

Related: Happy Death Day 2U's Ending, Time Loops, Killer, & [SPOILER] Explained

After spending weeks in the parallel dimension's time loop forced to continually relive her birthday, Monday, September 18th, Tree ultimately decided she had to return to her universe. She learned the necessary Quantum Mechanics to get SISSY to properly close the loop and jump her back to her proper dimension (after Tree unmasked and stopped the mirror dimension's new Babyface Killer). SISSY worked as intended and Tree was back where she belonged - and it was Tuesday, September 19th. But here's how Tree's happy ending got a new winkle in the post-credits scene that sets up Happy Death Day 3:

What Happens In Happy Death Day 2U's Post-Credits Scene

Happy Death Day 2U's mid-credits stinger shows that Tree really is free of her time loops at last. After she, Carter, Samar, Dre, Ryan, Dean Bronson (Steve Zissis), and the security guards woke up in the lab (with Tree once more back in her own dimension where Carter is her boyfriend), the group finds themselves doing community service picking up trash, no doubt as punishment for defying the Dean and causing SISSY's reactor explosion. As Ryan tries to explain to Dre how SISSY acted like a slingshot that pulled Tree back to her proper dimension and closed the time loop (and Samar ate a churro he found on the ground), a fleet of black SUVs arrived.

Agents of DARPA (Defense Advanced Research Projects Agency) led by Dr. Isaac Parker (Kenneth Israel) approached the college students and asked them to come with him. The group is brought to a DARPA laboratory where Dr. Parker reveals that he has "borrowed" SISSY and brought it to the lab (no doubt Dean Bronson was happy to be rid of it). Dr. Parker goes on to praise Ryan, Samar, and Dre for creating SISSY but noted his scientists don't have the right algorithms to get it working - something Tree suggests she can help them with since she spent weeks in her time loop learning Quantum Mechanics and eliminating all of the variables to find the right equation.

Tree also suggests a new test subject to be trapped in a new time loop: Danielle (Rachel Matthews), who the scenes cuts to as she wakes up in her bedroom screaming - obviously, she's now trapped in her own time loop, amusingly setting up the new victim of Happy Death Day 3.

What Does DARPA Want With SISSY?

Tree standing in front of a clock in Happy Death Day 2U

The invention of SISSY is an incredible breakthrough with huge ramifications, especially for a group of bungling college students, and it's understandable the U.S. Government wants to control the technology. The quantum reactor was intended to slow down time but instead, it has the power to trap a person in a time loop (albeit with bizarre horror movie-like rules where the day only resets if the person is killed). The applications of what SISSY can do have all kinds of possibilities - including being weaponized against enemies of the state.

Happy Death Day 2U's post-credits scene doesn't give much more than an inkling of what DARPA ultimately wants to use the technology for, but considering the experiment they want to conduct involves trapping someone in a new time loop, it's not a hard leap to make that there's an insidious plan for this tech unknown to Tree and her friends. And, despite the dozens of times she has been forced to die either by being murdered or commiting gruesome suicide, Tree didn't hesitate "volunteering" Danielle to be trapped in a time. Tree's not thinking about the dangerous big picture of SISSY falling into the wrong hands (and DARPA might already be the wrong hands); instead, she just wants some revenge on her frenemy.

Page 2: What Danielle's Time Loop Means For Happy Death Day 3

Danielle Is Now Trapped In A Time Loop

So thanks to Tree, Danielle is now trapped in her very own time loop at the end of Happy Death Day 2U's post-credits scene and this is a big clue as to what the story of Happy Death Day 3 will be. Being trapped in a time loop also likely means Danielle gets her very own Babyface Killer (possibly more than one since both Happy Death Day movies had at least two people wearing the mask). The Danielle who Tree trapped in a time loop isn't the one who dated Carter in the parallel dimension, but this Danielle is going to pay the price for that as well as for the bullying abuse she heaped on Tree and all of their sorority sisters.

Unlike Tree, Danielle probably doesn't have the wherewithal to figure out who her Babyface Killer is and eventually defeat the time loop. It's also not clear whether Tree, her friends, or DARPA will be able to monitor what happens to Danielle in the time loop. One possibililty for Happy Death Day 3 might be that Danielle simply can't free herself and dies horribly every time, which will result in Tree having to re-enter the time loop to save her frenemy from the punishment she herself inflicted on Danielle.

Related: You HAVE To See The Original Happy Death Day Before The Sequel

With Danielle as the victim, the possibilities of who her Babyface Killer could be will be different from Tree's. Could the second Ryan return? Will the girl Danielle bullied at the house meeting in the first Happy Death Day return to be Danielle's Babyface? The Babyface Killers in the first two Happy Death Day films were variations centered on Tree's roommate Lori and were linked to Bayfield University Hospital but Danielle doesn't have ties to either besides Lori (who is now dead) being her sorority sister, so the potential for who Danielle's Babyface could be opens up - and it could include Tree herself (or possibly, a Tree from a parallel dimension)!

What This Means For Happy Death Day 3

Happy Death Day 3

Happy Death Day has proved itself to be about escalation: Tree saved herself in the first film and she saved her friends in the sequel, so in third, maybe Tree will save the world? Regardless, Tree is the main character of the Happy Death Day franchise and the series is about Tree's arc as she grows and becomes a better person. Happy Death Day is rooted in Tree always being her own hero, and she's everyone else's hero as well. As the star of the Happy Death Day films, Tree always has to be the one who to face and kill whoever Babyface is. So there's no doubt that in Happy Death Day 3, despite her wishes, Tree will find herself caught in yet another time loop, either to save Danielle, fight Danielle's Babyface Killer, or both. And if an alternate universe Tree is Danielle's Babyface, then Tree would have to take on her own doppelganger, which would be another crazy sci-fi genre leap for the series.

Happy Death Day is now established to be in a sci-fi multiverse but the introduction of DARPA creates a new ally that could also become a potential new threat looking to exploit SISSY. DARPA hints at what could be in store for Tree and her friends post-college and it opens up the avenues that could affect their futures beyond September 17th and September 18th. While the third film will likely retain the franchise's signature time loops and Babyface Killer, Happy Death Day 2U proved the franchise's concept is malleable enough to go in just about any direction.

Writer-director Christopher Landon has said he has a "really bonkers and fun" idea for Happy Death Day 3 since he "always imagined Happy Death Day as a trilogy". This also feeds nicely into producer Jason Blum's desire for each Happy Death Day film to be in a different genre. Happy Death Day 2U took inspiration from Back to the Future Part II, and that franchise defied expectations by making its third chapter a Western. No doubt, fans can look forward to an equally unexpected but inspired genre twist when Happy Death Day 3 arrives to torment Tree with one last horrible day that won't end.

More: Happy Death Day 2U Did Avengers: Endgame Before Avengers: Endgame

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