6(Shadowhunters)

Shadowhunters version of 1(Multifandom)

So for some unknown reason Magnus, Alec, Izzy, Clary, Jace, Simon, Raphael, Meliorn, Maia and some others(up to the writer who else it could be) travel to the past to start the alliance between the whole shadow world sooner and deal faster with Valentine and all their enemies(if Jonathan may have his chance at redemption is up to the writer), etc.

Of course that everyone(and that everyone probably doesn't include the two sane ones, Alec and Raphael, but they will go with what the others want) decides that since they are in the past they can fuck up with other people especially the Clave because you know the Clave is shitty and none of them like them.

(This reminds me that the future they travel from must be before Malec adopt Max and Rafael as they wouldn't fell right by abandoning their kids and if something bad had happened to them and that was the reason for their return then everyone would take what they needed to do very seriously)

So imagine a few not nice shadowhunters when in patrols seeing the Lightwood-Herondale siblings holding hands with a mundane/downworlder and informing the others or directly telling it to Maryse and Robert which leads to a confrontation and the siblings act confused as say they only went out for patrols or the times Alec allowed the other two went to parties but never went on any dates only for people to still see it happen to the point some think they are hallucinating or there are shapeshifters going around.

They try to somewhat follow the original timeline for a few things like when Clary would make her discovery and get her memories back but once she did they started more chaos.

Like suddenly everyone would see one of the non-shadowhunter members of the time travellers in the Institute, walking around as if they owned it but if you looked away for a second, when you looked back they wouldn't be there.

When Valentine is announced to be back, the group discretely destroys his plans while letting Hodge hear their 'fake' plans to then watch how bad Valentine's plans go.

As Lydia appears, Alec asks her in marriage in front of his parents but in private he says that he doesn't want to marry her and plans to have Magnus take her place(Jem will be the officiator) to which Lydia is confused but decides to go for it since she is Magnus' fan and thinks it is kinda cool that Alec is going so far to marry Magnus while hoping their story ends better then hers with John(maybe they could save John...I'm not sure when he died in canon either way but you can assume that they would save some people who died like the youngest Lightwood or Ragnor if you go for show canon).

Also, the time traveller group goes around adopting any orphan or abandoned kid they find just because I imagine that after dealing with all their enemies they go to a Clave meeting and bring all their kids and go like 'Oh, right! We still haven't presented but this Clary and Alec' kid Xxx, that is Jace and Simon's kid Yyy, that one is Meliorn and Raphael's kid Www' but the kids weren't simply adopted by couples that were together, some of them were adopted by two that aren't together(like Malec, a couple, adopt Aaa but then Alec and Clary adopt Xxx because they feel like it not caring about supposedly only couples being allowed to adopt since they fake all the necessary paperwork...you can assume that if a social worker sees those paperwork they will be very confused and assume the time travellers are all in a poly relationship).

Anything else is up to the writer as it is if they decided to followed any of the ideas of the crazy and chaotic things they could do that I mentioned above.