Avengers Assemble (2012) #20
General Context - Infinity/Uncanny Avengers
The alien tyrant Thanos has invaded the Earth searching for his son, previously kept secret from him. In pursuit of this goal he attacked the Inhumans, a genetically manipulated offshoot of humanity with incredible powers. This prompted the detonation of the Terrigen Bomb, an Inhuman weapon designed to release the Terrigen Mists which empower the Inhumans across the Earth. The bomb succeeded, and the Mists are now travelling across the Earth awakening the powers of long lost descendants of the Inhumans spread throughout Humanity. Now the Avengers and the Inhumans are trying to find these newly awakened Inhumans to ensure they receive help with their new powers and aren't exploited by any malign entities.
Janet van Dyne is the Wasp, one of the original Avengers with the power to shrink in size and to fly and shoot bio-electric blasts while shrunk. She was an Avenger for years and is one of Earth's most experienced heroes, but seemingly died a few years prior to this when an alien pretending to be Hank Pym, a.k.a Ant-Man/Giant-Man and Janet's ex-husband, manipulated the Pym Particles which allow her to change size to make her a living bomb. In truth, she was trapped in the Microverse, an alternate dimension only accessible via shrinking. After an extended period surviving there by herself, Janet was able to signal the Avengers, who rescued her and brought her back to Earth.
Wanda Maximoff is the Scarlet Witch, a mutant with the power to wields hexes which can manipulate probability. A few years before this story, Wanda lost her mind due to the grief of losing her children and began tapping into dangerous, reality-altering power, a path which culminated in her nearly destroying the Avengers and almost wiping mutants from the face of the Earth. She was thought dead after this, but ultimately her survival was discovered and, after a conflict with Dr Doom, she dedicated herself to redeeming herself for her past failures (though without reality-warping power).
Simon Williams is Wonder Man, a former actor who was transformed into Ionic Energy and, after a short stint as a villain, became a superhero with powers of flight, enhanced physicality, and energy projection. After dying on a mission, he was brought back to life by the Scarlet Witch during her descent into madness, though at the time it was thought that he was always alive, Wanda just recombined his separated aspects. Following this he would remain a standard hero for a time, but would slowly begin to buckle in this face of numerous tragedies and failures for heroes. For a time he came to the conclusion that the Avengers as a whole were the problem and forcefully tried to stop his former allies, but ultimately he came to the conclusion that it was Superheroes' violent methods that he opposed, leading to his becoming a pacifist.
All three are members of the Avengers Unity Squad (shown in the 'Uncanny Avengers' series), an Avengers team dedicated to representing unity between mutants and the rest of Earth's superheroes through a combination of mutant and non-mutant members. In this team, the three have clashed around their complicated histories and conflicting motivations.
Terrigenesis, the process Inhumans undergo after exposure to the Terrigen Mists, involves entering a cocoon like the one shown.
Part of the concept of the Avengers Unity Squad was that they were a public facing team, which is likely why Dennis is quite familiar with Simon.
Lord Gouzar is a tyrant from the Microverse. Janet's inadvertently caused his downfall when she contacted the Avengers to rescue her from the dimension, as the team (including Janet) clashed with and deposed him.
Simon is familiar with Gouzar as he was on the Avengers team that rescued Janet.