When we last left our heroes, the Crystal Heart was discovered to be a real artifact, which they needed to find. Princess Cadance fainted due to exhaustion, causing her magic shield to vanish, and King Sombra was now advancing on the Crystal Empire...
...However, Shining Armor helps Princess Cadance to her hooves and she manages to conjure up the shield in the nick of time, halting Sombra's advance just before he can cross the threshold of the Empire's borders, and cutting off the tip of his horn. Shining Armor volunteers to find the Crystal Heart, but Twilight tells him to look after Cadance and sets off to find it herself. She tells Rainbow Dash to rally the others to keep the Crystal Ponies from discovering the fake Heart, and to keep the fair going to distract them from King Sombra's return, or else they will sink so far into despair that it won't matter if the real Heart is found. As they split, the severed tip of Sombra's horn sinks into the ground, causing a small black crystal to sprout.
Rainbow Dash informs the others of the problem, and Spike runs off to help Twilight. Applejack tries to keep the Crystal Ponies away from the still-covered fake Crystal Heart, while Rarity, Rainbow Dash, and Fluttershy do their best to distract the Crystal Ponies; Pinkie Pie, on the other hand, is distracted by the latter three. Their attempts are at first successful, but Applejack wonders how long their success will hold up. Meanwhile, the black crystal that sprouted from Sombra's horn begins to taint the surrounding crystals, while the barrier continues to weaken.
Spike persuades Twilight to bring him along—on the condition that he not lift a claw to help her, as per Celestia's instructions that only she can pass her test, which she now believes is to find the Crystal Heart. Reasoning that King Sombra was counting on the Crystal Ponies being too frightened of the castle to enter it, Twilight deduces that the Crystal Heart must be hidden there. Meanwhile, Rainbow Dash and Applejack struggle to keep the Crystal Ponies from uncovering the fake Heart. Applejack tells her to tone down on the aggressiveness, suggesting she show them her jousting skills, and Rainbow shanghais Fluttershy into a jousting match.
Twilight and Spike search through the castle, eventually entering the throne room where Twilight notices the throne is made of the same crystal that Princess Celestia used to show her how the Crystal Ponies' magic could be reflected across Equestria. Using the dark magic of King Sombra, she opens an underground secret passageway with a long, winding staircase that leads to a door at the bottom. After attempting to open the door with her own magic, only to have it constantly move around the walls of the pit, Twilight becomes infuriated enough that she uses dark magic on the door's gem at the top, causing it to open and emit a bright light. Twilight enters the door, delighted that she has found the Crystal Heart...
...Only to find herself standing in Canterlot's throne room, where Princess Celestia coldly tells her that she has failed her test. Twilight has no idea how she got there, but Princess Celestia says that it doesn't matter; she failed her test and will no longer continue her magical education. Twilight notes that Princess Celestia never said anything about Twilight not being her student anymore if she failed, but Celestia ignores her and walks away, leaving her staring at a window depicting Sombra's triumphant return. She is snapped out of it by Spike's voice, and she realizes that the door is enchanted to show ponies their worst fears. Twilight uses her normal magic to open the door again, this time leading to the base of the tallest tower of the Crystal Empire Castle... and more stairs. Spike reasons the endless staircase must be another trap, so Twilight reverses gravity, allowing the two of them to slide up the incline underneath the stairs.
Meanwhile, the other five are losing the attention of the Crystal Ponies, who are starting to swarm around the Crystal Heart to see it again. Pinkie Pie does her best to entertain them by juggling flugelhorns while balanced on a rubber ball. Suddenly, she slips and the ball knocks off the flag covering the fake Crystal Heart, and their ruse is discovered. At the same time, Cadance loses all magical power from exhaustion, and the shield vanishes once again. King Sombra's horn regrows, and the black crystal that had started growing now begins to duplicate and spread toward the castle. The Crystal Ponies notice and begin to panic, reverting to their previous dull coloration, while Shining Armor and Cadance can do nothing to stop his advance.
Twilight Sparkle arrives at the top of the tower to find the real Crystal Heart floating before her, and she steps forward to take it—and activates an alarm. Alerted to her presence in the tower, Sombra traps her in a cage of black crystals, but not before she manages to knock the Crystal Heart to Spike. Spike rushes forward to help her, but more black crystals sprout, blocking his approach. Realizing she may not be able to escape in time to prevent Sombra's attack, Twilight tells Spike:
Twilight:You have to be the one to bring the Crystal Heart to the fair.
Spike dashes off, climbing down the spires of black crystal growing from the tower, but King Sombra notices and forms a black crystal, which rockets towards the Crystal Heart, regaining his original form in the process. Spike slips and falls off the tower, but Shining Armor grabs Princess Cadance and throws her towards where Spike and Sombra will collide. Just before Sombra intercepts Spike, Cadance snatches Spike out of midair and they take the Crystal Heart to where the fake one was located. The combined power of Cadance—who the Crystal Ponies recognize as the Crystal Princess and the rightful ruler of the Crystal Empire—and the Crystal Ponies empower the Crystal Heart to send out a magical field of light and love, which obliterates King Sombra and restores the Empire to the way it was before, and in the process, transforming everypony in the vicinity into real translucent Crystal Ponies. Sadly for Rarity, this recent transformation lasts only as long as they are in the Crystal Empire.
The Mane 6 return to Canterlot, where a new stained glass portrait of Spike holding the Crystal Heart has been put up. Princess Celestia explains to Twilight that although she did not accomplish the task she was told to do, her willingness to see the deed through rather than accomplish it herself, thus attending to the needs of the many as opposed to herself, has allowed her to pass her test, and she can begin the next stage of her magical education. Twilight and her friends celebrate on the train ride back to Ponyville as night falls, revealing the aurora borealis that has begun to emanate from the Crystal Empire in the night sky. Princess Celestia and Princess Luna watch the train go, and Celestia nods at Luna, who summons a book with stars and swirls on the cover...The end.*Cue epic credits--happycredits music*
Tropes present in this episode and/or the preceding episode include: YMMV tropes here
Berry Punch, you are too drunk to be enjoying the jousting tournament!
For those wondering where the Derpy cameo is, she can also be seen at the jousting tournament, but she's partially covered by another pony and seen from the back. A few other regular background ponies also sneaked into the Empire, how they got there we may never know.
Casting a Shadow: Twilight imitates Princess Celestia's demonstration of King Sombra's powers in order to pass by his trickery. The first application works out very well. The second attempt triggers a trap.
Catch a Falling Star / Fastball Special: With Spike falling off the tower and Princess Cadance being too tired to fly up and save him, Shining Armor throws her at Spike to make the save and she glides down with Spike on her back..
Cadance's cutie mark has been a crystalline heart. This episode shows why.
Also Luna's black book at the end of the episode. It's revealed at the end of Season 3 that it's Star Swirl the Bearded's personal journal, and part of Twilight's test.
Chekhov's Skill: Celestia's demonstration to Twilight of what would happen if King Sombra returned back in Part 1 also gave Twilight the essential knowledge of using dark magic to reveal his hidden secrets and ultimately recover the Crystal Heart. And Twilight was able to perfectly replicate it after seeing it only once. She's that good at spellcasting!
Combined Energy Attack: The Crystal Heart combines the light and love of the entire Crystal Empire and turns it into an energy wave that blasts King Sombra.
A Day in the Limelight: While Twilight is the main focus, Spike still plays a huge role in the second part of this arc.
Dangerously Genre Savvy: King Sombra was extremely thorough in hiding the Crystal Heart and ensuring no one pony could find it. Only the presence of Spike allows victory.
To elaborate, he made the path to the Crystal Heart inaccessible without the use of dark magic, leading into a perilously long spiral staircase downward. At the bottom is a door that keeps moving around unless you blast it with dark magic as well, but trying to open it afterwards will result in a Lotus-Eater Machine. Even if you get snapped out of it and correctly open the door with other magic, you now have to climb an equally perilous and seemingly twice as long staircase up (unless you're Crazy-Prepared like Twilight Sparkle and have a gravity inversion spell to slide along the underside). Lastly, as a final measure, anybody who walks up to the Crystal Heart proper will become imprisoned in dark crystals. All in all, a very thorough protection plan, even assuming somepony had the courage and forethought to hunt it down preemptively.
Alternately, he could be considered dangerously Wrong Genre Savvy—the most deadly two traps are rendered harmless by bringing a single ally along. In a show where almost every significant threat has been met by a team of six ponies.
Decoy Protagonist: This episode is set up to focus on Twilight passing a test. But it's Spike who ultimately saves the day.
Despair Event Horizon: Twilight has the others keep the fair going or finding out King Sombra's returned to stop the Crystal Ponies from sinking so far into despair that finding the Crystal Heart won't matter.
The Dog Bites Back: King Sombra is finished off by the Crystal Ponies, who he himself enslaved and generally made life hell for. While the heroes set it up, the Crystal Ponies don't hesitate at all to finish the job.
Dungeon Bypass: One of the obstacles guarding the Crystal Heart is a spiral staircase, stretching impossibly high. Twilight realizes that climbing the stairs would take too long, so she casts a spell to reverse her and Spike's gravity, and proceeds to slide up the bottom of the staircase.
Earn Your Happy Ending: While the Mane Six DO do this (saving the Empire and Twilight passing her test is by no means easy), the ones who really do this are the Crystal Ponies. After being enslaved and emotionally crushed by King Sombra, they finally power up the Crystal Heart and destroy him for good, allowing them to finally be free.
Eureka Moment: Twilight realizing that the Crystal Castle itself wasn't Sombra's castle as it was back during his rule and that she needed shadow magic to reveal the Crystal Heart's hiding place.
Family Unfriendly Death: King Sombra is shattered to pieces. Even more shocking is if one looks closely, some parts of him hadn't turned to crystal. It's particularly noticeable in that he's the only villain aside from the Windigos to actually be destroyed.
Fastball Special: Shining literally throws his wife at the crystal heart. To be fair, it was either that or it end up in Sombra's hooves.
Foe Tossing Charge: Rainbow Dash knocks Fluttershy so hard with the Lance that she goes sky high without using her wings.
The MacGuffin for the Empire is a Crystal Heart that spreads love and joy. What's Cadance's cutie mark again?
Celestia and Luna can be seen holding a black book with stars and swirls on it, seemingly hinting that Twilight's studies are not over yet. The book with "stars and swirls" on the cover turns out to be Starswirl's "incomplete" spellbook, whose completion would be Twilight's final test.
It should be noted that when Cadance lands on the fake Crystal Heart with the real one, the identical crystal on her cutie mark is also glowing.
Freeze Frame Bonus: If one pauses when Luna pulls out her book at the end, one might notice starsandswirls on the cover. Seems DHX has been setting this one up since the start of Season 2.
Friend or Idol Decision: This is how Twilight passes the test. Twilight has the choice to either try to escape Sombra's trap and deliver the Crystal Heart to Cadance alone, following Celestia's test verbatim, or rely on Spike, who is outside the trap and closer to the Heart. Twilight chooses the latter, Spike saves the day, and Twilight learns the meaning of self-sacrifice.
Go Look at the Distraction: Applejack takes on the task of making sure none of the crystal ponies realize that the the Crystal Heart hasn't actually been found yet. Rather than lying to anypony who asks to see the Crystal Heart, AJ just changes the subject and encourages the pony to get some food, or check out the jousting show, or some other distraction.
Gravity Master: Twilight Sparkle specifically studied gravity spells in case they would be on the test. Turns out it was a good idea.
Happy Harlequin Hat: Pinkie Pie has an interesting variation that she wears; five colors and two flaps. The hat is green, and the flaps are purple and blue for the right and orange and yellow for the left.
Hoist by His Own Petard: Sombra's attempt to reach the Crystal Heart leaves him at the top of a several hundred foot crystal tower and reverted back to his pony form as opposed to his much more agile Living Shadow form, and thus with no way to escape the World-Healing Wave that follows moments later.
Karmic Death: King Sombra meets his end at the hooves of his own slaves when they power up the Crystal Heart and finish him off.
Killed Off for Real: King Sombra, and some say this won't be the last time a character dies on-screen in the show.
MacGuffin: The Crystal Heart, which Twilight needs to find to keep the Empire safe.
Mass Oh Crap: The Crystal Ponies' reaction to King Sombra showing himself.
Near Villain Victory: Sombra manages to come within a hairsbreadth of winning simply by planning.He even has his original body restored moments before Cadance gets hold of the Crystal Heart. If Cadance hadn't managed to secure the heart, everything would have been back the way it was before Celestia and Luna first defeated him.
Nice Job Breaking It, Hero: Pinkie Pie accidentally unveils the false "crystal heart" Twilight mistakenly made earlier, upsetting the Crystal Ponies.
Oh Crap: Fluttershy within seconds of getting the business end of Dash's jousting lance.
King Sombra's reaction to the Crystal Heart being powered up, though it's a good bit more subtle than previous villains.
King Sombra: What? No... No! Stop!
The Only One: Rainbow Dash and Fluttershy aren't on the castle's balcony when Spike and the Crystal Heart start falling, leaving Cadance as the only pony present who can fly. (Were they still making their way back from the jousting field?) However, after the Crystal Heart is restored and all the ponies turn crystalline, Rainbow Dash and Fluttershy are suddenly on the balcony with the others.
Sombra's mane is short, but it moves in the same way that Luna's and Celestia's do. This either confirms that it's power level, like Lauren Faust suggested for Luna, or it's simply because where Celestia and Luna are the Big Good, Sombra is a unicorn stallion that took on a form made of evil.
At the end of the episode, the power of the Crystal Heart gives everyone new hairstyles as well as making them crystalline.
Race Against the Clock: Cadance barely manages to put the shield back up, continuing the situation from part 1. Only a piece of King Sombra's horn is severed, beginning to spread his dark crystals inside the barrier.
As the Mane Six and Spike ride the train back to Ponyville, Celestia and Luna watch from Canterlot. Luna summons a book with a black cover embossed with stars and swirls. Roll credits.
Also, when King Sombra is defeated, we see his horn flying off in the distance. It's unknown if the horn's existence alone is enough to cause problems, or it may allow King Sombra to return at a later date. It HAS been shown that his horn can, on it's own, cause dark crystals to appear and independently work magic.
Spanner in the Works: If it wasn't for Spike coming with Twilight and helping her get through Sombra's traps and ultimately delivering the Crystal Heart to Cadance, King Sombra would have won.
Stealth Pun: After the Crystal Heart is activated and everyone receives a magic makeover, Twilight sparkles.
Stereo Fibbing: Applejack and Rarity can't keep their stories straight as to why they don't have the real Crystal Heart.
Surprise Slide Staircase: Inverted in many points. Facing a seemingly eternal stairway, Twilight inverts the gravity and turns the long way up into a fast slide "downwards".
Teleport Interdiction: Sombra's final trap protecting the Crystal Heart prevents a unicorn from escaping it by teleportation.
The Unchosen One: In the end, the one who saved the Crystal Empire was Spike, despite talk that it would be Twilight.
This Is Something She's Got to Do Herself: Twilight believes she must retrieve the Crystal Heart by herself as part of her test. Subverted when she has Spike bring the Crystal Heart instead of herself when she fears she can't make it on time.
Throw the Dog a Bone: Big time for Spike. He gets to be the hero, and he gets a stained glass window in Canterlot!
Triumphant Reprise: The Mane Six sing a reprise of Twilight's Failure/Success Song from Part 1, this time about how she's passed.
Weakened By The Light: The mere presence of the Crystal Heart is enough to banish King Sombra's amorphous cloud of darkness and corruption. When it's filled with the light and love of the whole Crystal Empire, it destroys him.
World-Healing Wave: The Crystal Heart emits one once powered up by the light and love of the Crystal Empire, undoing King Sombra's corruption and killing him.
Xanatos Gambit: King Sombra's booby-traps. Whether the pony reaches the Crystal Heart or not, they're screwed. This is doubly so in the present situation, as reaching the Crystal Heart lets him set off a trap that allows him to spread his dark crystals inside the castle even though the barrier was up.
Total trap count: Hidden entrance within the throne room. Doorway enchanted to both evade opening andMind Rape anypony capable of stopping it. Insanely tall spire to ascend. Booby-trapped platform that surrounds any intruders in black crystal, and nullifies teleportation magic. And of course, you need to be a unicorn who can use Black Magic to even get past the first one.
We'll put it this way: King Sombra almost won that episode, as there were only two things that truly defeated him. Shining Armor manning up at the last minute, and the presence of Spike. He almost won, simply by planning for most every eventuality.
Your Worst Nightmare: The visions shown by King Sombra's illusion spell. Twilight's hallucination involves Princess Celestia telling Twilight that she failed, and thus can no longer continue as Celestia's student. Spike's hallucination involves Twilight sending him away because she no longer needs him.
You Were Trying Too Hard: Twilight only manages to pass the test set to her by Celestia by giving up on passing the test for the sake of defeating Sombra.