WARNING: The following contains major spoilers for The Death of Doctor Strange #2, on sale now from Marvel Comics.
The loss of Doctor Strange has left those closest to him absolutely shaken, and they aren't the only ones. The murder of the Sorcerer Supreme brought both his greatest allies and enemies together in an effort to uncover the truth as well a slew of terrifying threats. The Death of Doctor Strange #2 (by Jed MacKay, Lee Garbett, Antonio Fabela, and VC's Cory Petit) revealed that Strange was the only thing standing between Earth and invasion by legions of supernatural beings. Now that Strange has been eliminated no one is left to hold them back, as evidenced by the mystic incursions that have already begun.
While Doctor Strange has always been one of the most prominent magic users in the Marvel Universe, it was his station as the Sorcerer Supreme that made him of utmost importance. As he has explained to the students of his Strange Academy, the Sorcerer Supreme acts as a safeguard between the world and the mystical forces that would do it harm. A younger version of himself has emerged to assist in the investigation of his death, but this isn't the Strange that the world needs right now. As he and everyone else gathered within the Sanctum Sanctorum learns soon enough, the death of his older and wiser counterpart has enabled the invasion of several supernatural forces.
Several mystical Marvel villains have already started to take advantage of the situation. The demonic Dagoth, once a servant of Shuma-Gorath, has risen his city of Kalumesh from the ocean floor to act as his base of operations, and the ancient Peruvian mage Tiboro reclaimed his former territory deep within the jungles. Additionally, Aggamon, ruler of the twisted Purple Dimension, has transported his fortress to the middle of the Gobi Desert, and Umar, the twin of the dread Dormammu, has materialized a portion of her kingdom in Antarctica.
From the standpoint of the Avengers, all of this amounts to a series of mystical invasions. However, the younger version of Strange notes that none of these "invading forces" have actually begun invading. Instead of unleashing their armies upon the world, they have all merely found a place to settle in for the time being, and that might be even more dangerous than a full scale assault.
None of the mystical villains who have appeared on Earth should be ignored, yet that is what this Strange seems to suggest when Captain America calls on him to help remedy the situation. The magic user finds the situation more interesting than anything, and he believes their presence indicates something much more sinister brewing beneath the surface.
The idea that something even more powerful than the amassed mystical forces may be waiting just behind the scenes is terrifying. Hopefully, this less prominent version of Strange will prove capable of handing whatever that threat may be, or at the least bring back someone who can.