Beams of electric-blue light began shooting down from the sky. Each one brought forth an enemy, directly teleporting them from someplace, and before William could comprehend what was happening, a new army had practically appeared all around them.

The enemies were humanoid, with short and squat bodies, but with large heads. Some wore nothing and had skin tones that ranged from pale green to dull grey, while others were dressed in outfits that looked like a hazmat suit with glowing blue visors.

"Cactuses! We've got Martians to deal with now?" Sid exclaimed.

"It's a trap!" Akbar the Dye Trader shouted.

The Grey Grunts ran forward, followed by some Martians with bubble shields surrounding them and some green Martians riding alien creatures that ran on four legs and had large, peeping eyestalks. Some suited Martians named Gigazappers held electric spears, which fired bolts of crackling energy. Some larger beams unveiled Martian Walkers, which were tall, mechanical vehicles that ran on three legs and boasted a lot of life and rapid-fire weaponry.

The citizens attacked, but they were surrounded on three sides. The Demolitionist's exploding pumpkins couldn't penetrate the bubble shields, while the ray gun blasts from the Martians began overwhelming any fire from the Arms Dealer, Steampunker and Pirate. William saw some Martians seemed to be setting up electric Tesla Turrets, which fired bolts of electricity that only added to their firepower.

He sprung into action, running forward and swinging his Terra Blade. Its energy swords could hit up to three enemies per shot, meaning he began to make some headway. He saw Meg firing her Razorblade Typhoon, the teal shots bouncing between many of the Martians and destroying them. Sid's Terraprisma got in on the action too, cutting the Tesla Turrets to pieces.

But even the Martians could counter them. The Tesla Turrets' shots seemed to inflict a deathly electrified effect, causing them to take massive damage. William noticed if he stood still on the ground while electrified he wouldn't take as much damage, but that wasn't really an option when there were shots being fired everywhere. Some flying Martian Drones flew directly for them, moving too fast to hit, and would detonate in an electric explosion upon getting close to them, again dealing lots of damage. He, Meg and Sid were forced to fall back.

William watched James in his Skeletron form trying his best to smash up the Martians, but even he was outmatched. Few of the Martian enemies were as large as him, but they boasted enough firepower and electric attacks to keep him from damaging them.

That was when one very large beam shot from the sky, unveiling a literal flying saucer that flew forward, a massive yellow deathray blasting out from beneath. It passed through one of Skeletron's arms, obliterating it, then began moving over the citizens.

"We need to fall back!" the Princess yelled as the Martian Saucer began raining a volley of laser fire from its turrets. The snowy ground was peppered with the blasts, several of the citizens getting struck or blasted into the air.

"You need to get back to the top of the wall at all costs!" the Wizard yelled.

"We're not going to be able to do that with that Saucer tailing us!" Meg shouted.

"Your highness, get the citizens out of here!" Sid yelled. "We'll deal with the saucer!"

The Princess nodded. She blasted at a charging Scutlix with her Resonance Scepter before motioning to all the citizens to follow her. William watched as they all ran towards the frozen lake at the bottom of the hill, one-armed Skeletron included.

But then the Martian Saucer zoomed right over their heads.

"It's going after the citizens!" Meg yelled.

"That thing could kill them all without suffering a dent!" Sid shouted.

The three of them began the chase, but the Saucer was already far ahead.

At the foot of the hill William saw one citizen had turned to face the alien ship.

It was the Wizard.

He held aloft an ice-tipped rod, and began casting magic that, somehow, actually began coating the Martian Saucer in ice. Its laser turrets became encased in ice blocks, and the bottom of the saucer where it fired its deathray began freezing over. Even its engines seemed to be freezing, soon coming to a stop directly over the Wizard.

"YOU... WILL NOT... PASS!" Merlyn shouted.

But even his magic could not stall the saucer forever. It fired its deathray forth, shattering the ice that had formed around it, straight down through the Wizard, obliterating him in an instant.

He had sacrificed himself, but the saucer had been stalled long enough both for the citizens to get far enough away, and for William and his friends to reach it.

"He should have said 'shall'," Sid said. "But I've got a plan. Follow my lead!"

He was first to attack, swinging out his Kaleidoscope whip at the Saucer's turrets, also sending forth his Terraprisma to attack it. William swung his Terra Blade at the Saucer, the energy swords hitting multiple turrets at once, while Meg's Razorblade Typhoon did the same. The Saucer shifted to a position low to the ground and began firing homing missiles at them. He and the others flew upwards to avoid them, making sharp turns in mid-air to avoid their tracking.

Before too long all the turrets and cannons on the Saucer had been destroyed. It shook a bit and even spun completely over, but then it began moving faster and more erratically, its deathray constantly shooting downwards. William dashed to the side to narrowly avoid getting broiled.

"Get on top of it!" Sid yelled. "I'll bait it!"

William and Meg flew upwards as the Saucer went for another pass, and they managed to land on top of its hull, grabbing hold of some grooves on the top.

William craned his neck to see Sid now running back to the wall and then grappling his way up, his jetpack propelling himself upwards very quickly. The Saucer kept on flying upwards, trying to get to Sid, while also erratically shaking to the left and right in an effort to throw William and Meg off, but they held on for dear life.

Before too long the Saucer had risen above the top of the wall. William could now see the entrance to the Dungeon, where Robyn stood, seeming to absorb the yellow energy from the mysterious hovering tablet.

He saw Sid's Terraprisma swords all fly up and stab downwards into the side of the saucer that faced away from Robyn. The impact caused the Saucer to tilt sharply at an angle, and its deathray ended up turning on Robyn.

From a distance William could barely see her reaction, but that was when the energy she was absorbing suddenly flared brighter, then shot back, pushing the deathray backwards like a movie where two powerful magic users were shooting each other with magic, connecting in mid-air, and trying to push their magic to the other to overcome them. Robyn's energy soon overcame the Saucer, blasting it to metal debris and throwing William and Meg off.

When William landed, he saw the Saucer had dropped an electric sword with a lime-green hilt, named the Influx Waver. He picked it up and stored it in his inventory, then turned to face Robyn. The mysterious tablet seemed to have shattered, its fragments littering the ground around her, but its yellow energy was still pulsating around her.

"You need to get your master out of your head!" William shouted.

Robyn just smirked.

"We know how your curses work," he went on. "You cursed James the Clothier with Skeletron."

"The bones of Cthulhu, ripped from his body by the race of Dryads," Robyn said, cupping her hands together to slowly form a ball of energy. "Skeletron was a reliable servant, until you defeated him. But I let that happen. I had someone else in mind, someone far more capable at the goals I needed to accomplish."

"And that person was Robyn," William seethed.

"Yes! Someone younger, but more weak-minded, vulnerable. Easy to take control of, exploit her worst demons."

He cringed.

"What are your goals?" Meg yelled.

Again, Robyn smirked. "I would've thought you would have figured that out by now. To restore Cthulhu."

"I know, but what about the mechanical parts you got the Mechanic to build? You threw them all at us and we destroyed them!"

"Cthulhu no longer needed them!" Robyn exclaimed. "But that didn't mean I had no use for them. I've tried to kill all of you. Several times. You are one of the only with the power to defeat Cthulhu."

"How come?"

"Because you defeated the world's Guardian."

When no-one else said anything, Robyn added, "When the Wall of Flesh was defeated, the Hallow was unleashed and the Crimson was amplified. The only reason this happened was so that the new Guardian could gain access to the tools they needed to properly guard their world."

All of a sudden it made sense to William.

"You're saying we're the new Guardians," he said, hardly believing his own words, but realising them to be true. "The four of us."

"Now you're catching on," Robyn said. "Cthulhu has been planning to return for some time." She pointed out at the battlefield. "The Pumpking and Ice Queen answered to Cthulhu, Lord of the Moon. As did the Martians, ever since Cthulhu turned his influence to their homeworld. They served their purpose."

"And the Lihzahrd? Their Golem?" William remembered Golem had tried to kill them due to seeking out his Lord.

To his surprise however, Robyn only shook her head slightly, but said no more on the subject.

"Nevertheless, all that is left... is for Cthulhu himself to come. He will bring the world under his will. He will destroy you all, as well as this body that I am possessing. He will... become the new Guardian."

That was when she suddenly split in two, a shadow of herself emerging out from behind her and rising up.

It coalesced, unveiling a person dressed in blue robes with gold trimming, and wearing a mask with a long beak.

The Lunatic Cultist.