Most of you have heard of iStudying and how well he does. He consistently either wins or loses only to Mr. R (which make sense) in regional tournaments, and against all odds he manages to do the same in national tournaments when there are others there, most notably getting 2nd at B.E.A.S.T. 6 over MVD and ESAM with pre-buff Greninja, as well as 3rd at Syndicate 2016 and several other top 32 placements including Pound 2016 and GOML 2016. But what a lot of people seem to forget is that there are tons of other players repping Greninja, most notably aMSa, Eddy, Elexiao, P2P with Gibus, Some, Techei and Venia, who all place top 8 pretty consistently around the globe and support his rep and results a lot. All of this proves that he has an amazing theory.
Really his only theoretical problem is that he falls fast, making him susceptible to certain combos, but he can always escape combos with Shadow Sneak, so that isn't too bad. His neutral is impressive, with quite high mobility, an amazing projectile in Water Shuriken, a fast walk speed to allow for safer grounded approaches, and a F-air that is very safe on shield. His landing game is pretty good, with a fast fall speed as well as F-air and mixups with D-air, Hydro Pump, and Substitute. His disadvantage state is good, too, with the aforementioned Shadow Sneak to escape combos or multi-hit moves as well as his quick Shuriken and excellent Hydro Pump, which is very fast and can change direction to be unpredictable.
And, of course, his punish game is lethal, with tons of combos that do lots of damage due to him having so many moves that have very little lag, and he can take advantage of footstools to start/extend combos and/or kill. Speaking of killing, he has plenty of ways to do so, including N-air or D-tilt into U-smash, footstool jab lock into forward smash, U-throw 50-50 into U-air (or true combo on platform), U-throw on its own at very high percent, D-throw 50-50 into F-air or a smash, using Shadow Sneak to escape a combo or multi-hit and punish, gimping with Shuriken or Hydro Pump, and occasionally upward Substitute on its own or into U-air.
Is he any higher than the lower part of high tier? Probably not, because it takes an immense grasp of the character and your opponent to take full advantage of all of this. But lower high tier is where he should reside at the moment especially after buffs, and right now I feel like he should be above most of the characters in his tier and alongside some of the ones in the tier above him.