About shinies

And just for personal curiosity, what would you do in my situation?

If you need a gyarados, take your highest level IV90+ magicarp and evolve it.

If you do not need a gyarados but want to have a red gyarados, just play on until you find a IV90+ shiny magicarp and evolve it.

The chances of it being great IV are probably so low, and 400 is a lot of candies to just say “Well I have a red one sooo….”. On top of crap IV what if it gets crap moves? Personally I would just save it for when trading comes out and trade it for straight up rent money. Yes money is worth more to me than imaginary fish.

I'd say it's worth evolving but powering up is optional.
Breeding does not guarantee another shiny. If Niantic follows the original games, the IV's might get passed down from the parent to the baby...but having low IV's and no guarantee of another shiny, why breed it in the first place?
I would evolve and place on gyms just for fun...not many people can say they have a shiny gyarados.

1. Depends...for completionist, yeah, otherwise no, but a red gyarados is cool.
2. No, it doesn't garantee that it's shiny.
3. No, there's no garantee, depends on how you breed and with what. You can arrange for the offspring to inherit up to 5 IV's from the parents (in the main game series there are 6) so let's say you have something like this:
   Parent 1: 5, 5, 5, 5, 5, 5
   Parent 2: 31, 31, 31, 31, 31, 31
   The offspring will have 1 random IV (any number and any of the IV's), and the other 5 will be either 5 or 31, this is the best case scenario, as out of the 5 choosen IV to inherit, there can be overlap, so instead of inhereting 5 IV's from the parent you can get only 2 or 3, because the same IV was selected twice, so you migth get 2 or 3 random IV's depending on luck.

If Magikarp candies are not a problem (meaning you have no problems shelling out 400 candies), then I'd evolve him but don't power it up. Otherwise, I'd just keep him as a trophy.

I was hoping they would have made shinies out of 100% IV only Pokemon or something similar so there wouldn't be this dilemma. I personally value IVs on a defender over how it looks, so it's doubtful I'll be placing shinies in gyms. It's up to everyone else to decide which they value more, unless you're lucky enough to find a shiny with good IVs. I think a shiny with good IVs will be extremely rare.

Do you have a low IV Raichu with a hat?

If so, you are most certainly a collector - absolutely grab the Red Gyrados! Sure, it's useless to you - but you will have one!

Gotta Catch 'Em All!

Some Pokemon are just like that - you keep them not because you are useful, but because you want to. Like your starter pokemon, or in my case, that Sudowoodo with Rock Throw just because I love the animation it has in battle...

As for me, I don't even have a Blue Gyrados yet (214 candies... Still collecting...)

Where does appraisal place its IV range?

Favorite it and wait till the end of the event. I'm guessing that chances of finding a shiny Magikarp/Gyarados will be pretty good this week, similar to past events with special spawns.

At the end of the event, if you haven't gotten another shiny at a higher level, you can evolve this one. You should be better able to calculate the Gyarados's IVs. Between the IVs and the moveset you can then decide if it is worth powering up.

Middling to good IVs and Dragon Tail might be worth powering up to show off in gyms. Bad IVs and Bite/Hydro Pump might still be worth powering up to 1000cp to 1400cp to at least use for prestige.

How can you tell it's a Shiny? I read you have to battle. Does that mean you have to put it on a gym or just when you battle on a gym you will see it's red? I'm confused.