Dororon Enma-kun Meeramera is more than just a fun anime. It's a love letter to Japan's Shouwa Era with its multiple references to old series and events etc. I will attempt to list all the references I personally found while watching the show. Keep in mind that the show's setting is 1973 Japan just like the original series. I don't claim the references are 100% accurate as I don't speak Japanese and I invite anyone with a better knowledge of the subject to expand on it.
* : Needs more information.
_ : Text is clickable.
This is based on GG's releases.
0:37: We have the Opening Theme sung by JAM Project Artist, Masaaki Endoh in collaboration with classic Japanese Rock Band, MOONRIDERS.
01:58: Harumi mentions a fuel shortage. She is actually referring to the oil crisis of 1973 which is the year the show is set in.
03:38: Renkonman is stocking on toilet paper. He's also referring to the oil crisis of 1973. "Price rises and unfounded rumors of a toilet paper shortage – based on oil being used in paper manufacturing – caused a panic and hoarding of toilet paper in late October and early November in Osaka and Kobe, among other cities."
02:36 & 5:00: The song played at those times is Furimukanaide (Don't Turn Around), an old song which seems to be from a TV commercial. *
05:22: This song is played in the original live action Harenchi Gakuen movie.
13:19: Kappaeru is doing an imitation of the Japanese YMCA by Hideki Saijo.
19:32: Enma-kun's hammer is an indirect reference to the director, Yoshitomo Yonetani other work, GaoGaiGar in which the titular robot uses a hammer known as the Goldion Hammer to destroy his enemies. The show aired after the Shouwa era in 1997, but it was included due to the connection to the director. It's to note that Meeramera is the only Enma-kun work to feature the hammer.
22.00: The Ending Theme is also done by classic Japanese Rock Band, MOONRIDERS.
09.38: When Enma-kun starts throwing girl balls, he's mimicking the Opening animation of the 1969 volleyball anime, Attack No.1. He even says "Demon Attack No.1" as a reference to the show.
09.50: Enma-kun is now mimicking the Opening animation of the 1974 drama anime, Alps no Shoujo Heidi.
At the beginning of every episode, the cast is shown in different outfits. These outfits are actually referencing past series as well.
Episode 1: Regular cast
Episode 2: Ultraman
Episode 3: American Comics
Episode 4: Ultraseven
Episode 5: Mirrorman, Fireman, Jamborg Ace.
Episode 6: Spectreman
Episode 7: Rainbowman
Episode 8: Tetsuwan Atom
Episode 9: Ambassador Magma
Episode 10: Thunderbirds
Episode 11: Journey to the West? Not sure. *
Episode 12: Kyojin no Hoshi