Some little tricks I've noticed:
S.Dio c.A3 into upwards knives. I'll have to test if this is avoidable but it seems pretty cool. If you tech you'll be forced to block the knives which gives him a guard break chance.
Chaka guard reversal links into his mid/high attacks which lets him combo Tandem. I already knew characters like R.Soul could potentially followup on a successful guard-reverse attack, but Chaka's doesn't seem to launch/sweep which is pretty interesting.
Mariah's guard reversal retains the same properties as her f+A2 it seems, as it is an overhead.
I find it interesting that a few guard reversals change depending on if your stand is active or not. While most of the cast's does not change, O.Joseph's and Chaka's actually do. O.Jo's inactive GR is his qcf overdrive, while his activated GR is his DP overhead swipe. Chaka's deactivated GR is his qcf+S sword, while his activated GR is the first hit of his qcf rekka. I'm pretty sure no one else's does unless you consider the Stand link/unlink differences for a few characters, like Iggy's and V.Ice's unactivated GR's are projectiles autonomous to them, but activated the character moves with the Stand, similar to Dio and Jotaro I presume.
The special move buffer window seems to be around 10-12 frames. In this regard, I experimented with pre-buffering guard reversals (especially after watching BBC's Chaka). And it is indeed possible. So if you first input a DP then hold down+back to block you have about 10 frames after the down+forward input to input an attack command for the guard reversal. Unfortunately 10 frames isn't how much you really get for down+back because you need to account for the time it takes to go from down+forward to down+back. I could test how many frames is it but precise numbers in this matter don't seem relevant and I can't think of any other excuse to do so other than "because I can".
Activating a Stand's Tandem then immediately going for a throw as soon as the stand disappears is pretty amusing, though I'm sure you'd have to read your opponent pretty well. But I'm thinking there may also be some option select possible here, which is pretty devious if it works.
I've known since the first time I experimented with Hol Horse's rdp super that it had the potential to be unavoidable, since it's an unblockable projectile. Sure enough, that super is pretty much guaranteed in a number of situations which you can reliably react to.
Speaking of unblockables, several characters have access to unblockable simultaneous high and low hits like in SFA3. That's one of the things that makes Vanilla Ice so ridiculous, aside from his airmovement and ridiculous pokes anyway. His qcb move is actually an overhead and acts autonomously of V.Ice, allowing Ice to hit low while the stand hits high at the same time, thus creating an unblockable hit. The same applies to Devo whose qcb move is also an overhead and acts autonomously of Devo. However, the same is true for anyone that has a stand tandem that can hit low, since while the Stand is hitting low the character can be hitting high.
I assumed that like SFA3 the mechanic of air supers canceling out tech recovery time applied in Jojo's as well. However, it seems that you are able to act almost instantly (perhaps instantly) out of a tech anyway so the super isn't really doing anything special to the tech window, other than being a super anyway.
Some characters have normal moves that move them forward quite a bit which can be kara'd into Stand/Special/Super of course. Mariah A3 canceled into stand or qcb is a good example, or Chaka c.A3 canceled into qcf+S is another. But I don't think anyone has a kara-throw in Jojo's since it would seem all the characters with command grabs lack forward-moving normals, unless you could O.Joseph's slide attacks, which I don't personally since they don't begin moving forward until the active attack frames.
Regarding Mariah's back+A2, the knife appears after 10 frames. Seems like a good safety measure when performing her laggy projectiles out in the open. For example if you set her stand on or near the ground then back+A2 then dp+A3, the back+A2 can protect you to some degree from an opponent trying to jump over the outlet. Good thing that move is not an overhead.
One of Midler's primary BNB combos involves linking an unactivated attack to an activated attack. Pretty simplistic since the Stand activation is freely cancelable. This allows her to do like: dashing c.A1 c.A1 c.S+A1 c.A2 A3
Wherein the S+A1 is an activation into immediate activated c.A1. Fortunately the link window is large enough after her unactivated c.A1 for this to be possible.
But several characters can/need to make use of this. Chaka and O.Jo use activation switches during their Tandem combos, and I'm sure other characters make use of it too.
Stands really remind me of Personas. I don't know why I hadn't associated the two previously, they are essentially the same. I'm not sure if it's an homage or not, but the Tower stand in Jojo's writes on the wall "Massacre", and one of the highlighted Personas in Persona 1 was Tower_Massacre. I should probably ask Rithli about this.
Speaking of which, before I forget, I was musing with Rithli over who else from the 3rd arc of the manga could have been added in as a playable character.
Of course the first that jumps to mind is the Tower. The user wasn't given a name in the manga but apparently he's just a joke-ish sort of battle in the PSX version.
I also feel Moon could have appeared as a playable character. The user was Tennille and put up about as much of a fight as the others, so I don't really see why not. Kind of reminds me of Aulbath anyway. But once again he was fated to be a joke-ish storymode character in the PSX version.
Empress showed up in the PSX version as joke storymode. They would totally have to improv the user's fighting style like they did for Midler though, and find an excuse for her stand to be fully formed at the start of a battle.
Rithli insists Strength could be a character. Yeah right, that thing would have to be like a mid/sub boss or something. So would Justice for that matter.
But more importantly I think the worst waste of a character slot was not putting N'Doul with Geb as a playable character. I certainly think I'd prefer him over the Hol Horse+Boingo and S.Kakyoin clone characters. Alas, he is fated to be a joke-ish storymode character. But I think he could easily have been a Sogetsu clone. It's not like they've never had a blind character in a fighting game before, hell S.Kakyoin is supposed to be blind(ish).