The black, demonic depiction of Mazinger Z in certain scenes is the titular demon of Mao Dante.
Episode 2: Most, if not all of the delinquents seen with Boss are random thugs from other Go Nagai works, such as Devilman.
Episode 6: The bomb that Count Brocken unleashes on the city is not other than Groizer X, another Go nagai super robot design!
Episode 7: In the flashback, we see photos of the archaeological team that was searching for Bardos Island. Many if not all of them are cameos from other Go Nagai works.
Episode 9: Tsubasa mentions a priest visiting from "Daemon in Abashiri." Daemon is one of the main characters from Go Nagai's manga Abashiri Family.
Episode 10: Ankokuji's line "Kurogane House is turning into a Shameless School!" is a reference to Go Nagai's breakout manga, Harenchi Gakuen (Shameless School).
Cross is partly based on Naojima Abashiri from Abashiri Family. Their cyborg forms are almost identical and both were voiced by Tessho Genda.
Episode 13 features various weapons from Devilman and Violence Jack, including Jack's knife, the Slum King's samurai armor and the anti-demon special forces armor.
Episode 13 also has Kouji call Count Brocken "Count Decap", which was his name in the Tranzor ZMacekre.
Episode 16 has Baron Ashura address the audience in the same manner as Akira from the later part of the Devilman manga.
Oddly enough there's a Ken Ishikawa reference in ep 19, Ashura appears very simillar to Ryoma Nagare from Getter Robo Armaggedon (who was in turn based on Shinichi from Maju Sensen)
Also in episode 19: the shot of Zeus holding his arm in his mouth is identical to what Jack does in the Golden City arc of Violence Jack. Since this was the arc that featured the original Tsubasa, it can't be a coincidence.
Episode 23 features a giant statue of Devilman in the hotsprings.
Episode 24: Similar to Boss' gang, the Kurogane Mob consists of random thugs who have appeared in various Go Nagai manga, such as Violence Jack.
When Discotek Media licensed and released the show on DVD in the U.S., they released it under the name Mazinger Edition Z: The Impact!, as requested by the original licensors.
Made its debut in Super Robot Wars Z2, though even before this was announced, the franchise was explicitly name-dropped by the mechanical designer, who said he was requested to come up with an "all new, awesome MAP attack" for Mazinger — the Big Bang Punch. When the God Scrander shows up in Z2 Saisei-hen, it does indeed have a MAP version of the BBP.
From that point on, Shin Mazinger became the default Mazinger representative of Super Robot Wars series, only missing out on UX (which uses the debuting Mazinkaiser SKL instead) and X-Omega (which uses the classic Z and Great, as well as the Mazinkaiser OVA). Some notable mentions are:
BX, where Mazinger-Z God Scrander and Mazinkaiser SKL Wing Cross have the "Dynamic Combination," and this version of the Great General of Darkness becomes Suddenly Voiced and the final boss of the Shin Mazinger storyline.
V, where Koji gets to pilot Mazinger ZERO, and this version of Tetsuya turns up alive and gets his own SRW-created upgrade, "Mazin Emperor G." Not to mention the Emperor of Darkness appears as the final boss of the Shin Mazinger storyline.
X, where Koji gets to pilot the original SRW-created Mazinkaiser, which can team up with Tetsuya's Mazin Emperor G to perform the "Majin Soukougeki" on Mazinger ZERO.
Fan Nickname: "Shin Mazinger Z" is never used by the series, but fans use it to distinguish the Shin version of the mech from the original.
It's also used for the show itself. The actual title is "Shin Mazinger Impact! Z Chapter", but everybody just calls it "Shin Mazinger Z".
Talking to Himself: The Latin-American Spanish dub used a very small pool of VA's, so this trope took place many times. i.e. Alan René Bressant had seven roles including Professor Morimori, Boss, Professor Yumi and Professor Kenzo Kabuto (the last two have almost exactly the same tone).
What Could Have Been: Energer Z is actually based on Go Nagai's original concept sketches for Mazinger. In the original drafts, the pilot would use a motorcycle and a bridge on the back of the robot to ride up to the cockpit and control the super robot. Nagai's editor told him to change it to avoid accusations of ripping off Kamen Rider.