I wasn't here for the 3ds days and I constantly hear about this mythical Greninja, can someone actually tell me what was going on with him that made him so broken?
Greninja was essentially a different character in 1.0.3 (the 3DS days). Firstly, his Usmash had ten fewer frames of end-lag, the side-hits did 2% more, and the hitbox itself was one unit larger, making it
much harder to punish when spaced while also still being very powerful for a sourspot. Against a lot of characters, it was a move that very difficult if not impossible to punish (it essentially only had 22 frames of endlag) while giving a huge reward (Usmash sourspot actually had more knockback/damage than Dsmash sweetspot; it's killing a CPU Fox 11% earlier in Training mode. It was killing at 89% on ledge against Fox and 104% on Mario, and even without DI, that's also without rage on the larger 3DS FD blastzone).
Secondly his shuriken had seven fewer frames of ending lag, meaning he had a projectile, one that he could combo off of full charge no less, with only 19 frames of endlag on ground (his air shuriken was untouched in the patches). While his aerial shuriken might be better now, his ground shuriken was really incredible because it allowed Greninja to put even more pressure on opponents than he currently does. He simply can't do as much out of shuriken now as he used to (we used to be able to get free grabs out of full charged shuriken as long as it hit the opponent, and knowing that, I'm sure we would be able to find a
lot of other things we could get out of it). Also, for some reason, he couldn't be grabbed during end-lag of shuriken.
Thirdly, Hydro Pump could straight up just block some Up-Bs head-on. Even if you weren't in helpless and going toward the stage, it pushed you back pretty far. It had a massive nerf, obviously, which really hurt Greninja's off-stage game. It's also worth noting Hydro Pump could be used as a follow-up to Uthrow if they were too high to Uair since it had a good chance of pushing a lot of characters past the top blast-zone. It was a bit gimmicky, but it did snatch KOs.
Fourth, Greninja's Uair KBG was reduced by 22. This move used to kill people at 120% from the middle of the screen, much like Sheik's Uair can do now. In fact, had it not seen that reduction, it's likely Greninja would have had his own hoo-hah as vectoring was a big reason as to why Uthrow to Uair wasn't an extremely powerful option on 3DS (could just simply vector the Uthrow upward in order to have more of a chance/time to escape the Uair). However, even without that combo, Uair was still very scary due to Greninja's fantastic jump height. Also, every hit of Uair until hit 6 auto-combo'd, whereas now, hit 5 has its own separate, unique hitbox that hits opponents up slightly, meaning it is possible for floaties to escape it pretty easily, especially if Greninja has rage (Luigi in particular actually always gets sent into tumble from hit 5 once Greninja has near-max rage, popping him far above hit 6). Now, you're lucky to see Greninja's Uair kill someone at 80% even if they're in the magnifier while being hit by it. It actually now has less knockback than one-turnip Villager Uair or Bronze Sword Robin Uair.
Finally, another gimmick, but Greninja could interrupt all landing lag with Shadow Sneak (which in itself was a risk given Shadow Sneak's massive end-lag back then). Made attempts to punish his landings, especially Dair, somewhat risky.
Fair also received a nerf by having its KBG reduced by 8, which made it kill less reliably as well. His hurtbox was also made larger, which indirectly made the Fox MU much worse as he could no longer crouch under lasers (he is now always forced to approach Fox regardless of who has percent lead).
Improvements he didn't have back then that he does now: Dsmash doing 2% more universally, Shadow Sneak having less end-lag, Shadow Sneak's shadow moving faster, Ftilt having ten fewer frames of endlag (that's where those ten frames were taken from =x), Ftilt damage increased by 0.75, Ftilt has a sourspot on the thigh (???), Shuriken coming out five frames faster, Dthrow has seven fewer frames of end-lag (that's where those seven frames came from as well I guess) and does 1% less (allowing it to combo better and be useful), Fsmash KBG improved by two, sweetspot of Usmash KBG being improved by one, Shadow Sneak KBG improved by four, Hydro Pump bounce no longer being a death sentence, three fewer frames of landing lag on Fair and Bair, one fewer frame of landing lag on Uair and Dair, standing grab comes out three frames earlier (total amount of frames unchanged), and dash attack comes out two frames earlier (total duration is two frames faster).
Opinion stuff, feel free to correct if I'm wrong:
Still think he was just a tad better back then just because of how strong those nerfed tools were, but I prefer him having the more balanced character design he has now.
I still think the most damaging nerf ended up being his Usmash, even if it's a nerf I 100% agree with. The move was an extremely powerful tool, especially combined with Greninja's mobility (and it would be even worse had it remained as it was after the shieldstun change). As a Greninja main, I don't really begrudge the nerfs, though, because it forced us to get creative with the character, and I think that's resulted in a much more dynamic character than what he might've been if most of us were able to simply rely on his overtuned tools to succeed at low or mid levels of play.
Greninja was a bit of a mess at release, and in some ways (hit 5 of Uair, blindspots on Smashes), he kind of still is, but I'm pretty happy with where he's at now. I'm not sure how his meta would've progressed had he not been nerfed, with many stating he had strong out of the box tools making him seem extremely strong on release, which draws comparisons to Brawl R.O.B. and G&W for me (who both were seen as strong characters at first but fell off due to atrocious MK MUs and also because we found ways to get around those tools), but he seems like a pretty strong contender now, with everything in his kit now having some kind of use that isn't overshadowed by a different move in said kit (even Sub has its moments).