Another great episode!
The palpable uncomfortable "atmosphere" in the alien-created subspace was well created and maintained with lurid colors and fisheye camera perspectives.
The boxer alien's original form with the weird saucer-shaped head and eyestalks appears to be a take on an Ultraman monster, Kanegon.
Kanegon is relatively well known for a Ultraman monster
Kanegon is associated with money (Okane == money in Japanese), which sometimes transforms humans into Kanegon form, which makes the Dan Da Dan-version's "salaryman" motif appropriate.
The upgraded boxer alien's form has a similar profile to the Baltan aliens from Ultraman,
And the Serpo aliens' white with black geometric stripes resembles the Dada aliens from Ultraman.
The Ultraman Dada aliens also kidnap human specimens for unknown research purposes, and are associated with the number 3, having 3 faces.
The Serpo aliens' profile resembles alien Pegassa once again from Ultraman