The plan was a combination of simple elegance and amazing complexity. Malygos had retreated to a pocket dimension, a place where he controlled the flows of magic. They could not beat him there. He was in control. So the plan was to instead bring him out of it.
The simplicity of the plan was that all they had to do was bring him to the ground, where a hole Poldaran was working on opening would lie, ready to take him out of that dimension and into the normal world, with a bit of a fall waiting when he went through the hole.
The complexity of the plan stemmed from how they were to accomplish this. Each person had to play a role. Envinyata, Sharlot and Xelsia would be harassing him by buzzing around him and unleashing their most painful attacks, thus leaving Malygos susceptible to the chains that the others would try to bind him with. Envinyata and Nuna would ride the flying platforms that they had stolen from a storehouse nearby and use the shadow to sear Malygos while Sharlot and Xelsia would assume their Stormcrow forms and fire bolts of lightning at the Blue Aspect. Fennchurch, Nephelim, Raequann and Waste would all be throwing enchanted chains with grappling hooks at the dragon, attempting to tangle him up and bring him down.
Yoxutre had a more difficult job. He was to use the Spear of Hodir to chain himself to Malygos so that he could steer the dragon to the hole as it came down. He was to do this by hitting the beast as hard as he could with his mace in the direction he wanted it to go. When Poldaran had handed him the spear with a wicked smile on her face, he had groaned. Everyone had heard the story of how he had, under some strange influence of the spear, used it to bring down a Wild Wyrm in the Storm Peaks for no other reason than the challenge of it. Not one of his prouder moments. In fact, thinking back, he thought it was rather silly of him.
At first, things went exactly as Poldaran had said they would. Yoxutre was able to chain himself to the dragon, and due to the spear's magic, Malygos couldn't shake himself free. The ground team was able to easily get the chains hooked to Malygos, thanks to the air team's distractions. Unfortunately, Poldaran had forgotten to tell them that they needed to hook the chains to the ground near the hole she was opening so that the chains would direct Malygos into the opening.
So, as often happened when she forgot the details of a strategy for a fight, Poldaran was forced to improvise and shout somewhat panicked commands during battle. "HIT HIM WITH THE HAMMER TIL HE FALLS!" she shouted at Yoxutre. "START TARGETING THE WINGS!" she commanded the air team. "TRY TO GRAB THE CHAINS AND DRAG HIM DOWN!" she ordered the ground team.
Yoxutre laughed. "Alright," he said to himself. "'Hit him with the hammer' it is, then." He began pounding away at the spot between the dragon's wings with his mace. It was as good a spot as any to hit. He noticed that the others had begun concentrating their fire on the wings as instructed. After a while, Malygos began to fall.
Unfortunately, the ground crew had been unable to reach the chains, and the dragon was falling the wrong way... off the platform. "Crap!" Poldaran shouted out, unsure as to how to react. She began gathering her will to attempt to pull the falling dragon the way she wanted, but knew it wouldn't be enough.
"On it!" Envinyata shouted. The dwarf priestess guided her flying platform past the dragon at breakneck speed and performed a near instantaneous stop. She then flew full bore at the falling dragon and slammed into it with the platform's bottom, effectively kicking it upward and in the other direction. There was a slight miscalculation on the force of her kick, however, and the dragon was now on course to fall off the other side of the platform.
One of the Stormcrows screeched, and the other screeched back. They flew above the hole and waited until the flying dragon was in the perfect position. They then shapeshifted into massive Moonkins and sat on the dragon with a prejudice, thus correcting its course one last time in a general hole-ish direction. As they approached the dimensional hole in the platform, Yox wisely unchained himself and dove off.
A few moments later, they heard a dull thud as the dragon slammed into the icy ground below.