Time travel? Creature inheritance for hp
Parring Elsa possible mate au?
Either twin or femharry Belladonna Hogwarts learns about both eras in classes. The wizarding world thought that the dragon riders had a bloodline ability for dragon taming and that Elsa has one for ice and just didn't use her magic for anything else and won't settle for anything to disprove them. Set after Belladonna wins the war so she is the Master of Death who stops aging at 21 and a dragon shifter this causes her to specialize in fire magic later as a side affect not to mention her high body heat. Belladonna's creature inheritance activates a couple months after she dies it's part of why she will go through the Vail of death the other part could be cause she is tired or something to do with her magic or if you want you could go the bad Dumbledore and co route. After going through the Vail she ends up in Hiccups time were he is a baby so he grows up thinking of her as an older sister. Belladonna could be Gothi's(the old lady) helper and maybe because of this the village ignores the fact she doesn't age. Belladonna is only allowed to use her magic besides potions in case of emergency to maybe justify the dragon attacks still happening? Here the options on time travel split option 1 Before the second movie of HTTYD and before Frozen Elsa could stumble on a time rift on a night walk and appear in the spot where Hiccup first met Toothless where the riders their dragons and Bella(dragon queen because she is a shifter so she's stronger then any dragon Toothless is second in command) were having a picnic which causes Elsa to have a panic attack for 1 it's day 2 she's somewhere different and 3 there are strangers and dragons which she has only heard of from myths and stories/history books. Here Elsa loses control and causes Bella to step in and calm her after she is calm Elsa apologizes and calls herself a freak which triggers Bella and causes her to snap at her in a reprimanding way and show Elsa her powers herself. Elsa while surprised soon becomes excited cause she is not alone even if there not exactly the same and hugs Bella cue embarrassed duo and laughing adopted little sibling group over the second HTTYD movie Bella and Elsa grow closer and learn each others stories and Elsa could become Bella's rider (😑 you know who you are) the httyd group don't learn that Bella is immortal till the 3rd movie they just though she was long lived because of her dragon shifting maybe they could become immortal from a potion using Bella's blood anyway, along the way of the movie Elsa learns control and deals with her issues though this and her age if she is physically older then Bella and doesn't take the immortality potion to be in the same age range as Bella gets set back after Bella studies the time rift though no one goes through it till Hiccup and Astrid's kids are at least 18 if you go that route either way the dragon den (big whole in the ocean) gets warded by Bella maybe you could have the dragons become immortal 2 through a ritual to connect them with thier riders so that way everyone has thier dragons in Elsa's time and beyond. For the first Frozen movie after going through the rift everyone appears the morning after Elsa disappeared or a week after but a month before her Coronation so they have time to discover Elsa's set back though Elsa is anxious she is not full blown panic attack cause she has her anchor(Bella) to help her again she still loses control you can decide why it happens. For Frozen 2 Bella could be the spirits guardian/protector maybe Anna and Kristoff and stven become immortal after learning they could still have a family and not out live them if they wanted that was. If you want you could move on to the original harry potter time line with a new prophecy about Bella and co raising Harry? Option 2 for split time travel have the httyd movies happen first and have everyone live through time till Elsa's time and maybe Bella becomes a queen with Hiccup as crown prince though Bella's inner circle now this is unnecessary of a well known magical kingdom in other words everyone knows her kingdom has magic/powers the duo could meet at Elsa's Coronation and hit it off so Bella stays and helps during everything. You could have Hiccup take over for Bella who takes a vacation during the second Frozen movie and fo from there.