[It's Super Effective]

Suicune used Hidden Power Ground while holding choice specs

[Gym Leader Serra.]

There's always Magmar with Sunny Day (think)

[Vitamins]

This video has the 5th sticker:

https://www.youtube.com/watch?v=pHVnJGde_KI

[Magnezone: Episode 10]

In Episode 10.1 the rock is breakable, so therefore you have to download episode 10.1 in order to get the key

[yureyu key puzzle. help!]

I found that the strength pattern was straightforward, just push only one strength boulder down each hole and follow the natural pattern and soon youll get to the part with 2 ladders beside each other and get there. Sorry but it was the best way i could explain

[Meet the Gym Leaders!]

If you find all the police officers before you beat the PULSE in Beryl all the panels have to be turned to blue in Corey's Gym

[Battle Strat. 101(Spoilers)]

I've never had any trouble with any of these battles

El - Have a Scrafty (for the 4x dark resist, but a 2x resist can work as well, the first I did it was with a 2x resist and it worked just fine), any Ghost Type (a mon with sturdy would be very nice but not required at all), repeatedly switch until El runs out of attacking PP (crits dont matter that much), next your ghost type should use curse, after the curse spam will-o-wisp so El with have to use his 3 full heals, so after the 4th will-wisp you can switch out (if necessary) to your fighting type and spam strong fighting moves if you dont have setup (HJK is the best), or setup if you have a setup move, Arceus will eventually have to struggle (if you havent beat him) and there's your win.

Serra - Have a pokemon with Sunny Day or Drought and GG that s what I found

Noel - Have a Scrafty and Magneton(w/Sturdy), Scrafty for everything other than Swellow/Staraptor, In my battle Noel legit U-Turned his staraptor into my magnezone's discharge.
(Note: the first time i did this was with Blaziken, if cinccino uses HP, bulk up twice, if not bulk up once and you'll still OHKO everything except Staraptor)

Aya - Psychic Types put in massive work especially gardevoir.

Florinia - Special Fire moves will work until her cradily, start off cradily with strong fighting moves until she uses curse, then come at it with special moves, my kadabra worked wonders on it even with being frail.

I've never done the optional sirius fight.

These strats are what I've done through 2 playthroughs, first one was casual second one I was trying to speed through it.