Several things involving Nico are references to stuff that her voice actress Mage likes.
Nico liking Ghost and jumping to Takerus defense is pretty much how Mage reacts when anyone talks negatively about Ghost.
When Emu and Asuna first meet Nico, she can be heard humming the Zyuohger theme. Mage, despite having mixed feelings on the show itself, adores Yamato Kazakiri and has referred to him as her husband numerous times. Mage also plays Amu in Chou Super Hero Taisen: The Abridged Movie.
In episode 5, Nico remarks that TV Tropes put Emu under The Friend Nobody Likes. At the time the episode came out, the TV Tropes page for Kamen Rider Ex-Aid: The Abridged Series did have an entry for that trope, but it stated that everyone somewhat qualifies to each other and only specifies Takeru as a particular example among the cast. It was not until after the episode was released that the TV Tropes page was subsequently edited to make Nico's statement accurate.
During a cast commentary, Emus voice actress pointed out that a TV Tropes contributor misheard her line in episode 5, saying that the teal Ex-Aid actually calls Super Mario Sunshine archaic rather than arcane (see Sophisticated as Hell on the main page). Like the above example, the page was soon edited to correct the mistake.
Played straight with NICO NICO ★ RIDE FEVER. In it, she mentions that its been three years since theres been a female rider, obviously referring to Kamen Rider Marika. However, before Nico transformed, Alia transformed into a Ridernote Albeit for less than one episode, and in the actual show, Poppy transforms into Kamen Rider Poppy a whole two episodes before Nico has the chance to become Ride-Player Nico.
Episode 8 has Kamen Rider Poppy state that her stats are equal to Fruit Jesus. According to the supplementary information that this line is referring to, the ability parameters of Kamen Rider Poppy are actually more than three times that of Gaims Kiwami Arms, not equal.
Poppys voice actress Mana is one of the creators of Yu-Gi-Oh! ARC-V The Abridged Series. The other creator, AzzyFox, played Kouta in episode 4 of Ex-Aid Abridged and voices Ren Amagasaki in this series as well.
Mentioned above under Actor Allusion, Kiriyas voice actor HyperJacob96 is a significant contributor to the online rap battle community, making his own rap battles and even working on the team behind Epic Rap Battles of Pokémon.
ProtoDubs and SpecialForm12 have toku podcast called Bugster Bros, and often end each episode with an improv skit playing their characters from Ex-Aid Abridged. SpecialForm12 is also known for making translations and fansubs of various toku media, like next episode trailers.
Aside from voicing Yoshitaka, Zony11 used to be a typesetter for TV-Nihon's fan subs.
Despite the joke of ProtoDubs voicing everyone, the rough cuts of Chou Super Hero Taisen Abridged played in some streams show that Marcos accidentally forgot to include ProtoDubs in the ending credits. This was noticed and fixed before the final cut was released.
Kanon, Edison Damashii, and Grandma Fumi only have one line each in the entirety of Kamen Rider Ghost: The Dead Abridged Series. Their voice actors, Mage, SpecialForm12, and Surrounded by Perverts, are the only members of the cast who actually like Kamen Rider Ghost, making their limited presence in the abridged series rather ironic.
Loads and Loads of Roles: ProtoDubs voices a lot of characters, including Hiiro, Hiiros dad, Another Hiiro, Parad, Graphite (from episode 3 onward), and Onari (from episode 2 onwards). This video takes it Up to Eleven, having him do every character's lines in episode four and claiming that his recordings are edited to sound like the original voice actors after the rest of them died, leaving him to voice everyone.
Magnum Opus Dissonance: While the fanbase has criticized episode 2s reliance on what could have become Overused Running Gags and catchphrases and generally feels that the show started Growing the Beard around episodes 3 and 4, ProtoDubs favors episode 2 specifically for those exact reasons of establishing the running gags and catchphrases.
The trailer for Chou Super Hero Taisen Abridged has a line from Another Hiiro about working at a homeless shelter, but this was omitted from the final cut because Marcos wanted to be more subtle in characterizing him as a better person than the real Hiiro.
Kaito has a line in the trailer for Kamen Sentai Gorider Abridged that references the Gaim Abridged Oneshot, but it wasn't in the actual special.
The deleted scenes video includes lines for Emu that were recorded by a different voice actor before Madds McCool was cast.
The Totally Radical-speaking Ride-Player in episode 8 was supposed to be voiced by Surrounded by Perverts, but Marcos had forgotten that his lines were already submitted months prior to the episodes release and had GlennShiraishi record them at the last minute.
Harutos voice actor XenoBlazeVA also recorded lines for Young Haruto in Wizard X Decade, but Young Haruto is voiced by Surrounded by Perverts in the final cut.
The two Dans, father and son both voiced by SpecialForm12, spoke to each other in Cards Against Humanity.
The TokuSins video for the Brave special had ProtoDubs get kicked out of his chair by Hiiro, who he voices. For that matter, this is in full effect in the ProtoDubs voices everyone video.
During a stream, Emu and Makoto had to share a room together. Both are voiced by Madds McCool. They spoke to each other again in Chou Super Hero Taisen Abridged, with Emu and Yakumo also falling under this in the same movie.
In some of the videos on his personal channel, HyperJacob96 occasionally has the characters he voices in Ex-Aid Abridged interact with each other and/or with him.
In his Q&A video, Kiriya appears and ends up arguing with Jacob. Saki also appears, but both Kiriya and HyperJacob96 tell her to shut up, causing her to cry.
Another video by HyperJacob96 had Stinger (who he voiced in Chou Super Hero Taisen Abridged) and Kiriya trading jackets.
In his review of a bad "My Little Pony vs. Pokémon" rap battle by Animeme Rap Battles, Kiriya shows up near the end to call BS on Jacob's claim that he could probably make a rap battle as good as ERB's if he had the $10,000+ budget that "MLP vs. Pokemon" was made on, stating that Jacob would most likely spend the money on Orbs in Fire Emblem Heroes. Jacob retorts that it'd still be a better use of money than what Animeme Rap Battles made with it.
ProtoDubs has Loads and Loads of Roles, so it's only natural that his characters end up talking to each other at some point.
Ever since Graphite started being voiced by ProtoDubs, his ghost talking to Hiiro falls into this. This also comes into play with Hiiro and Another Hiiro in Chou Super Hero Taisen Abridged, with Another Hiiro even speaking to Graphite's ghost.
A case of this in the original Ex-Aid that was averted in the abridged series. When Emu splits into the two Mighty Brothers, they speak to each other. Rather than both Ex-Aids being voiced by Madds McCool just like Hiroki Ījima voiced the both of them, Maddie only voices the teal one. According to his voice reel, ProtoDubs is actually the voice of the orange Mighty Brother (i.e. the one that Parad eventually becomes).
Word of God: Some of the voice actors for the series are tropers and will reveal official details by hiding them on TV Tropes itself, though youd have to look into the edit history and figure out whos who to know which statements are from them.
Mage has said the reason Nico's transformation phrase changed from Its Nico time! in episode 5 to Let's play! Kamen Rider! Modulation! when she actually transforms is because she was so inspired by Taigas heroism that she let go of her grudge against Emu, and wanted to show him that he didnt have to fight alone.
Mage has also written a short prequel for Nico, explaining what her life was like before she met Taiga.
Writing by the Seat of Your Pants: The abridged series was in its planning stages while the original Ex-Aid was still airing, and released its first episode about two-thirds of the way into the seasons run, so some details from the initial plan had to be changed to accommodate developments in the actual series, like Nicos prominence and Graphites revival.