Starting with episode 8, the anime used some of the settings from the existing music videos, starting with using exactly the same song and dance as the very first release (albeit shortened to fit).
The scene where Eli joins in episode 8 is copied almost exactly from the 1st PV, just with speech this time.
Episode 10 has Hanayo's rice in a bowl.
Hanayo's call for help at the end of episode 6/start of episode 7 is repeated with all of the first years in episode 12.
The second season opening theme is full of these with short animations of the girls based on BD covers of the first season. The ending theme also has a few visual call backs to the first season ending, most noticeably the repetition of the girls standing in a line with Honoka singing at first, then the rest joining in and shaking maracas. Also the part where Honoka give her hand to a viewer is pretty much the same way she did in 4th PV.
At the start of 2nd season, Honoka throws the microphone upward in the same fashion as she did in the 4th PV, albeit mirrored.
The ensuing Disneyesque sequence also features the exact same scene with Nico and Maki from the 1st PV.
In episode 1, Honoka is once again eating bread under the same tree with the same ensuing phrase, "Man, the bread today is delicious as usual!" from Season 1 Episode 1.
Fast forward to episode 6 season 2, during the scene where the group impersonates each other, Nozomi, as Honoka, says this exact line in her best impression of Honoka's voice. It's even lampshaded.
Nozomi (as Honoka): Man, the bread today is delicious as usual! (eating bread)
Honoka: Is that how I usually am?
Also in episode 1, Honoka once again ditches her jacket and bag, and does the same run towards the camera with it spinning as Season 1 Episode 1, this time in the shrine. The group also sings the opening lines of Susume—>Tomorrow.
In episode 2, the girls break into groups of three to brainstorm ideas for their new songs. These groups are all subunits of μ's that have released singles.
In episode 3, Honoka verifies that by "μ's", Hanayo means the protagonist idol group and not the soap brand. She made a similar comment when the group name was suggested in episode 2 of the first season.
Also in episode 3, Rin is sent after Nico, who was running away. Rin was also the one who chased Nico when she tried to run away in her introductory episode in season 1.
She's also sent after her in the following episode. Nico lampshades this in episode 5 season 2 when she locks Rin in the practice room before she can run away, giving her reasoning as "Because Rin is always the one who chases after her."
In episode 5, the beginning repeats the gag from the first season where Honoka loudly yells about them being at the ocean (pronounced "umi" in Japanese), only for Umi to tell her not to yell people's names (this joke was Lost in Translation in the English subs.)
Also in episode 5 of season 2, Hanayo and Maki push on Rin's back to encourage her to be the center, mirroring the shot from the first season where Rin pushes Hanayo on the back to join μ's.
For a little while in episode 8 season 2, the girls try to simulate romance using a video camera and a "giving chocolate to the audience" scenario. The ones with Hanayo and Maki reflect scenes from the "Mogyutto 'love' de Sekkinchu!" pv.
The girl's sleepover clothes in episode 12 are the same ones used in the "Music S.T.A.R.T." PV. They also invoke the song's title as their pre-performance cheer line.
μ's encore performance for the Love Live finals is the entire "Bokura wa Ima no Naka de" OP sequence from the season 1 frame by frame.
Before doing the encore performance, as she hears the audience's demands for an encore, Honoka recalls her words to Eli after μ's first live (which had not much of an audience) in episode 3 of season 1, which stated that even if the audience aren't cheering for the then-newly formed μ's, they still want to do their best so they can get across their feelings. The difference is that this time around, they are watched by so many fans who simply adore them.
Honoka's father criesagain after watching μ's performing live in episode 12, just like in the first season finale.
Kira Kira Sensation's dance sequences are a combination of all of μ's previous songs & PVs.
The ending theme for the final episode has Kotori randomly photobombing one of the scenes. This is a reference to the Season 1 opening.
During episode 13 where the group was looking around the school for the last time together, as they stopped in the alpacas' stall, Kotori still found the white alpaca so fluffy and played with it, just like she did in episode 4 of season 1. On the other hand, Eli once again finds out that the brown (female) alpaca is not too friendly, especially to her, a reference to episode 8 of season 1.
Same episode, different scene: Before Honoka leaves the rooftop, she recalls the conversation of herself, Umi, and Kotori about how the rooftop is the only option for their practice place from episode 2 season 1.
Just like in Season 2 Episode 5, Umi lost to Kotori in a game of Old Maid due to the world's least convincing poker face.
Kotori — once again — did her signature photobomb during Bokutachi wa Hitotsu no Hikari.
Umi is worried that Kotori might've forgotten something before the group's flight to New York. Kotori says there's nothing to worry about and brings up her pillow, which is what she forgot to bring in the 5th PV.