Within the Marvel cosmology, there are four primary sources of mana when it comes to casting magic.
The first is one's own life energy. If a mage chooses not to burn their own lifespan, the spells cast using only this energy are highly limited, usually restricted to minor spells like astral projection. The second type is the natural energy of the material world, which is also quite limited if relied upon exclusively.
The third type is external energy, which is what most high-level sorcerers utilize. The sources of this energy are diverse, and because the energy is often too boundless, it can easily cause harm to the sorcerer themselves. Of course, one can find ways to mitigate this damage—for instance, by communicating with and requesting aid from a powerful entity residing within those dimensions, typically its ruler, known as a dimensional Hell-Lord.
Generally speaking, dimensional Hell-Lords will not refuse your request, because the mere act of being petitioned grants these abstract entities power. The more their concepts and names are uttered within a reality, the stronger they become in that reality, and the stronger they become overall. Naturally, some dimensional Hell-Lords demand additional conditions. For example, the Vishanti require their followers to preserve reality.
Then there are malicious entities like Chthon or Belasco, who demand the caster's soul as a price.
"So, generally speaking, if you are not a powerful sorcerer, it is best to switch to a different source of power. If you are a powerful sorcerer, you can choose to beat them up and force them to change the toll to a simple, ordinary price, or simply steal their dimensional energy without ever mentioning them in reality."
Strange spoke with considerable familiarity, chatting with Wanda while flipping through the Necronomicon. Wanda decided to temporarily ignore the phrasing "beat a dimensional Hell-Lord up" and continued to ask, "And then what?"
"And then? Then, if Belasco intends to cast a spell, where will his source of mana come from? Although he is a follower of Chthon, he would never sell his own soul to Chthon, and other dimensional Hell-Lords are unlikely to accept a summons from a follower of Chthon."
As for his own dimension, Limbo? It had already been seized by Illyana. As long as Illyana and her Darkchild version were not wiped out by Belasco, Belasco would have no way to draw power from Limbo.
"Because of this, Belasco's source of mana must come from necromancy. This is Limbo, the so-called edge of hell, the first circle of Dante's Inferno. Countless souls plunge into this place, and it accumulates an immense amount of energy generated by the termination of life itself."
And the energy generated by the termination of life happened to be the casting source for the necromancy invented by Chthon—the absolute best source of mana for black magic.
After listening, Wanda suddenly looked at Strange. "Wait, wasn't Dante's Inferno a piece of artistic fiction?"
"It is based on factual events, though not entirely accurate. He was a great sorcerer of his time, a hero who stopped Belasco from summoning Chthon into our world and exiled Belasco to Limbo."
As he spoke, Strange explained the reason he carried the Necronomicon. "Therefore, I must prevent Belasco from utilizing this energy. White magic repels most forms of life energy, especially this kind derived from the dead. Meanwhile, the Darkhold is linked to Chthon; using it now might accelerate Chthon's descent. Fortunately, I picked up a copy of the Necronomicon earlier, which can be used to resolve this dilemma."
On the other side, the half-team of the Midnight Sons charging toward Belasco were still discussing the situation as they advanced. Even Blade, who usually remained silent, couldn't help but inquire, "Does that sorcerer really have no other means of dealing with Belasco? I've dealt with plenty of vampires, but I've never dealt with a fellow like that."
Beside him, Moon Knight was utterly puzzled. "Then how did you end up joining this team?"
"Because the elder god that guy wants to summon is the creator of all vampires. Heh, I intend to see exactly what kind of holy terror this entity is."
As they were speaking, another tremor suddenly shook the earth and shattered the mountains. Initially, the Midnight Sons thought the summoning ritual for Chthon had entered its next phase. However, what emerged from the ground was not molten lava, but skeletons and rotting, twisted hands. A massive horde of undead creatures and wraiths surged from beneath Limbo, rushing headlong toward Belasco and the Darkchild.
Belasco, who was in the middle of performing the summoning ritual, felt the shift. Strange had used some unknown spellbook to execute a massive, terrifying, and powerful undead summoning ritual, completely monopolizing nearly all available mana. Belasco's face darkened as he looked up at the sky. Fortunately, it was primarily Chthon himself who intended to descend now.
But the problem was that he could no longer cast spells himself. Unless he sold his soul to Chthon or burned his own lifespan, he would have to rely entirely on his physical prowess and swordsmanship to combat these undead creatures.
And this was the first grand gift offered by Strange.
In the sky, Spider-Man was still continuously tearing open rifts in reality. Strange shook his head and then fixed his gaze upon the sky. Right now, practically everyone except Wanda had a task assigned to them. With nothing to do, Wanda could only look up. A vast amount of lava was continuously erupting from the sky toward the ground, and this lava was rapidly repairing the rifts in reality torn open by Peter.
Immediately afterward, the lava transformed into a sort of living existence, beginning to hang down in large quantities like droplets of water about to fall.
However, this process ground to a sudden halt.
"Excellent, our 'reinforcements' have arrived." Strange let out a sigh of relief. "Originally, the timing wouldn't have been this tight, but unfortunately, Mephisto didn't show up. Otherwise, Spider-Man could have kept the rifts open a bit longer, and Chthon's infiltration of Limbo would have been weaker."
"What exactly is your plan?"
"Do you see those hanging 'droplets'?" Strange looked at the dangling matter. "Those are a part of Chthon's essence descending into this world—a very, very small fraction. He is currently being held back by someone, so he will remain hanging there like that for a while instead of falling. What we need to do is prevent him from falling normally, and instead rip that fraction away from Chthon's main essence."
"And how do you intend to do that?"
"First, we must withstand Chthon's next wave of attacks. This will be a retaliatory strike, because he must have realized the very instant he entered Limbo that this is a trap."
As Strange spoke, he put away the Necronomicon and drew the third spellbook he had brought along. "Fortunately, I brought the Book of Vishanti, the book of the gods of white magic. It has sensed Chthon's presence."