Development Gag: Carried over from another work with Billy Dee Williams as Two-Face. He never got to play the role in the Batman film series, as while he played Harvey Dent in Batman, Tommy Lee Jones took over as Two-Face in Batman Forever.
The Daleks aren't voiced by Nicholas Briggs, who voiced them in LEGO Dimensions and has been their official voice since 2005. Some archived recordings of Briggs are used, though.
Despite being in the main cast as Alfred, Ralph Fiennes doesn't voice Voldemort. Word of God is that they considered it, but it then would have been pretty much mandatory to contrive a scene where Alfred and Voldemort have a conversation, and it didn't seem worth the effort.
The Latin American dub is a special case: Unlike with other animated adaptations involving Batman or the DCAU, this is one of the few who wasn't dubbed in Venezuelanote Partly because this is a spinoff from another movie, who was dubbed in Mexico previously, and also because Mexican laws forbids dubbed films in theaters with non-Mexican dubs, albeit this is not always enforced. Keep in mind other Lego's animated films involving Batman were dubbed in Venezuela, but dubbed in Mexico instead. This become even more bizarre because there's another dubbed version used exclusively in Colombia, but only Batman and The Joker were dubbed by Colombian voice actors. The rest of the cast are still voiced by Mexicans.
In a much straighter example of this, none of the voice actors from the Latin American dub from previous film reprised their roles here, albeit many of them reprised their roles from their respective live-action films they appeared previously.
The same goes in the Japanese dub, as Takehito Koyasu reprises his role as the Joker from the dub of Suicide Squad (2016). Also, in a very bizarre twist on this, Kōichi Yamadera (Batman) reprise that role from both the Japanese dubs of the previous movie he appeared and also from the 1989 Batman film, which was broadcasted by TV Asahi in the 90s. In the same way, Hikaru Hanada, the regular voice actor for Superman in the dub of Superman: The Animated Series, also reprises that role in the movie, and being the only Japanese VA from the dubs of the DCAU who reprise his previous role here.
Averted with Ralph Fiennes, who is in the movie, but as Alfred, not Voldemort.
Concept art shows drastically different designs that were considered for some of the characters, including a hipster-esque Riddler, a literal Robin Hood outfit for Robin, and a Tommy Lee Jones version of Two-Face.
The Nightwing outfit Dick dons during the final battle was originally much closer to the suit from the comics, even including the classic bird emblem.
Batgirl, Commissioner Gordon, Catwoman, and Two-Face were all intended to be white at various points in the film's development.
Some concept art has also revealed villains that didn't make into the final cut, including the Ventriloquist, Hush, Doctor Double X, and Silver Banshee.
Had Ralph Fiennes voiced Voldemort's cameo here, he would have gotten a scene with Alfred to play off the fact that they were voiced by the same man.
A sharp ear might recognize that both members of Garfunkel and Oates are in this movie; with Riki Lindhome as Poison Ivy & The Wicked Witch of the West and Kate Micucci as Clayface.