While the show was just announced, the show's Twitter account asked fans who they would want to play these characters. There was an overwhelming response to the idea of Simon Lewis being played by his actor in the movie - Robert Sheehan.
Due to the unpopularity of the first film The Mortal Instruments: City of Bones (2013), The Mortal Instruments: City of Ashes was cancelled and it was later decided to reboot the series in a television format.
Alberto Rosende's character Simon Lewis in Season 1 episode 2 refers to Dominic Sherwood's character upon first meeting him as "this Mick Jagger looking guy". In 2012 Dominic Sherwood played Mick Jagger in the Not Fade Away
In the tv show, they have many computers and electronics at the institute, but in Cassandra Clare's new book, Lady Midnight, it says that the clave "Resisted the advent of modernity, but even more so any engagement with mundane culture"
In several promotional posters for the series, Emeraude Toubia's pose (complete with whip in the midst of being cracked) is almost identical to that of the cover art for the early games of the Castlevania series, which features vampire hunter Simon Belmont as the protagonist.
Season 1 of Shadowhunters is rated 12 in the UK (with the exception of the finale which is rated 15) for moderate violence and threat, whereas Season 2 is rated a 15 for strong violence and gory scenes.
The trivia items below may give away important plot points.
The director and others have been rumored to be adding more in-depth scenes of the relationship between Magnus Bane, High Warlock of Brooklyn, and Alec Lightwood, Shadowhunter. In the behind the scenes documentary, The Making of Shadowhunters: Beyond the Shadows, there is a brief showing of the script for episode 12. It is titled Malec which is the ship name for Alec+Magnus.
Warlock/Shadowhunter, Theresa "Tessa" Gray has been mentioned two times throughout the series; when Magnus is speaking to Elias in episode four, Raising Hell, he tells Elias to tell Tessa to put up the wards and in episode 12, Malec, Tessa is on the list of three warlocks that could have put the spell of Jocelyn, along with Catarina Loss and Ragnor Fell.