The scene of Dagur hesitating outside a tent to possibly meet his father is very similar to a scene with Zuko and Iroh, the latter of whom was originally voiced by an actor who Faustino's Korra character was named after.
Channel Hop: Due to Cartoon Network having changing channel expectations (using more 2-D Canadian material and later, filling the schedule with nothing but reruns of Teen Titans Go! for a time because, depending on who you ask, it was cheap to make and very profitable, or was, and still is, a tool used by the Moral Guardians allegedly running the network to artificially lower the ratings of the older-skewing series to justify shitcanning them), Dragons season 3 was moved to Netflix as Dragons: Race to the Edge. Unfortunately, the first 2 seasons weren't moved with them right away, leaving questions about who all the other characters around Berk are.
Dawson Casting: JB Blanc plays Ryker, the older brother to Viggo, who in turn is played by Alfred Molina. Molina is actually fifteen years older than Blanc, though he doesn't sound it.
Executive Meddling: Cartoon Network's censors didn't allow much show of affection between Hiccup and Astrid in the first two seasons, limited to ship teasing and a single kiss. When the series moved to Netflix, it was free of the censors and could now openly portray them as a couple.
Fake Scot: Nolan North as Stoick and Chris Edgerly as Gobber replicate the Scottish-Viking accents of the original cast.
Fandom Nod: The couple Hiccup and Astrid are given the nickname "Hicctsrid". This is brought up in "Shell Shocked, Part 1" by Snotlout.
I Knew It!: There was seriously a lot of doubt Alvin was killed by the Skrill.