Timid is preferred on a Offense boosting Pokemon in general. Nasty Plot is already giving you a 200% stat boost which makes a beneficial nature's 10% boost fairly redundant.
As cool as Brave Bird it, Blaziken doesn't really need the coverage it provides. Overheat is nice to have as it allows...
I'm honestly not too fond of Tailwind for ingame use. It's nice, yes, but given how quick ingame battles end up being, I find a long-term stat buffer like Tailwind to be more than it's worth. I'd honestly keep Roost as Talonflame is going to be killing itself fast with the dual STABs you've...
I just went for 252 Speed EVs on Pikachu because I legit cbf to do the calcs. I don't really see the need to change it, though!
My argument against using Mega stones is that I don't want to destroy the game too easily. I'll slash it in regardless!
I'd run a purely Special Greninja by giving it Dark Pulse > Night Slash.It's SpA stat is inherently much better than it's Atk stat so unless you have a +Atk nature Dark Pulse is the better choice.
Rock Slide / Fire Fang is the better third move on Garchomp. Crunch doesn't give Garchomp any...
I'm only using Blaze Blaziken (lol) because it's the one that Birch gives you at the start of the game and I make it a thing to make my first game completely within itself. Unless ORAS changes things Flannery should still give you the Overheat TM so go nuts with that!
I wouldn't mind playing it...
Blaziken @ Leftovers / Blazikenite
Lonely Nature (+Atk -Def)
Blaze (Speed Boost)
252 Atk / 4 SpA / 252 Spe
Flare Blitz
Hi Jump Kick
Thunderpunch
Overheat
Going for a MixKen set as opposed to the standard SD set, reason being that +Atk Blaziken's Physical STAB moves are able to run through...
I talked to a mod about it and it looks like it'll be down for a while. He did promise that what would eventually appear will be worth the wait though!