Also, before that, Master Tierra's revelation of her fate. Tried to control a Fire Mystic, only to get imprisoned in Mana-Dampening Armor for the rest of her life. Imagine, living your whole life in armor, trying to find a cure while being helpless to do anything else.
In the next episode, the ghouls that try to get into Allie's house. Allie's mom/Megaria drugs the kids, and they wake up, seeing The Undead coming towards them, and no matter what they do, they just don't stop coming.
Even worse when Allie's so terrified at what she's done that she runs to the Darkness Realm to find Megaria for help, and when she sees Ray, Gabe and Squeaky, she attempts to try to kill them all, even nearly killing Ray with the Cloak if it weren't for him to meet the Darkness Mystic and using the Spell of Ultimate Darkness to escape.
The whole premise of "Exchange Program": Not only are Light Civilization creatures abducting and replacing a number of people, they're also using a form of Mind Control on the abductees to alter their way of thinking to better match the Light-Realm's fixation with order. And then they start projecting the mind-altering beams all over San Campion, with their Queen hovering over the city, along with a large number of Light soldiers. That's scary enough for those who know about Kaijudo and what exactly they're seeing, but imagine how scared everyone else would be!
Everyone's abuse on Tatsurion when he was a kid.
The Choten's harvesting of Rumbling Terrasaur horns.
Also, Shouter's flashback as to how he lost his tusks.
From the same episode, the increasing Body Horror factor of Saguru and Humunculon's mutation, as well as the fact that Humunculon seems to be gaining more and more control and influnce over Ray's father.
The fact that The Choten and Megaria, who rival only each other in regards to being the worst villain in the series, are working together now!
The look on the Choten's face when Alakshmi uses Razorkinder to break his Tech Gauntlet and pin him to the ground. The spinning face of Razorkinder doesn't help.
Master Brightmore's face and reaction to seeing Duel Master Tiera alive, all because he inadvertently caused her presumed death.
The Body Horror factor of Saguru's and Humunculon's mutation is even worse now, with Ken now in an almost feral state, which only the presence of family members can snap him out of. It's getting hard to tell he was ever human now, and Lord Finbarr says that this happened with him attempting to treat Ken's condition.
The aftermath of the attack on Fire and Nature by Water. Not only did the Butterfly Effect wreak havoc in San Campion, but the two civilizations are devastated! Allie even says that San Campion got off easy compared to the destruction in the Creature Realm!
It's even says that many in the initial path of the attack didn't survive.
In "Siege", the attack on the Temple. The Duel Masters didn't even see it coming.
Megaria's completing the curse that she cast on Jaha decades earlier, leaving Jaha ancient and decrepit - in fact, barely even alive - before Jaha banishes her back to the Darkness Civ. using the her cane - which is actually the remains of Megaria's brother's arm!
The Choten's plan for the Fuel Tanker. It was to be dropped off like a WWII Bomb to evolve every Creature. He then uses a powerful Gauntlet to control them, and with Terrasaur Horns, he invades the Earth in the way Optimus Prime would fear.
The Duel Masters trying to fend off the attack the Choten makes, all of whom are below power and can hardly stand a chance.