A Tonberry vs. Sin

[Carl the Llama]

Title says Tonberry vs Sin, not Tonberry vs Sin and Sinscales.

You're right, it says Tonberry, not Don Tonberry. Also I would mention that when you fight Sin on the Ship to Killika he uses Sinscales to attack, he has no other moves other then to hurl the Sinscales at the ship, so they are a valid form of attack. I also notice how you failed to address the shield he has, does that mean you concede the point?

If Sinscales are a form of attack, they are vulnerable to counters, so the Tonberry will easily hit Sin with Voodoo and Karma.

Ahh but what you are forgetting is that the counter would be dealt to the Sinscale, not Sin himself. If you use cheats to hack on Counter Attack during the fight where Sin uses his Sinscales to attack, the counter would be dealt to the Sinscale, not Sin.

If you are going based on what it says in the title, then I would counter with Giga Graviton, to which regular Tonberry is not immune to. Sin would just charge his Overdrive bar like he does on the fight on the Airship, doing no moves just boosting, then he would unleash his overdrive and kill regular Tonberry just like that... all the while Tonberry would be helpless to do anything.

Voodoo instantly kills any Summoned Aeon. Sin is an Aeon. Sin dies.

Technically the being Sin started out as a Final Aeon, and as such are unlikely to be subject to the same rules as a regular Aeon, aside from that Sin itself was changed into armour as stated by numerous sources throughout the game, in the transformation there could be any number of changes. Thirdly you're wrong about Voodoo being instant kill:

If the player summons an aeon, it will attack with Voodoo, in which the Tonberry creates a small stone statue of the summoned aeon, then stabs it, dealing 9999 points of damage to the aeon.

Curious to whether or not Master Tonberry had death attached to its Voodoo (as it doesn't give details on the wikia), I loaded up my recent playthrough of the game and whipped out Anima (who had 14k HP) and used Shield and when I did MT dealt 2500HP damage, ok I thought, let's see what happens when I use boost? 9999 Damage... which just happened to fill my entire Overdrive and I unleashed it upon him... needless to say he died. So after this we discover it's only the Don Tonberry that has death attached to Voodoo, and then it is only a chance of death, not certain (because that is what it says on the Wikia). I might mention that it is only Don who is immune to gravity, so if and when Tonberry uses Voodoo, it would still only deal 9999 damage, and as Sin would be boosting it could very likely fill his entire Overdrive to be unleashed on our green soldier.

Plus Sins shield is even more powerful the a regular Aeon, note that during operation mi'ihen the machina failed to penetrate it, let alone do any damage.

In short even if he didn't use Giga Graviton he could easily do this:

Step 1: Shield
Step 2: Sinscales

There is no way he would be able to defeat Sin.