can you use this spell to reverse flesh to stone?

You'll want Greater Restoration for that.

If you pair flesh to stone with stone shape you can shape a person's head off then stop concentrating on FtS then they come back and it's a auto kill.

Also is the con save against my spell save DC because most of the time in spells they specifically say it is but this time they didn't.

If there is no specification, it's assumed to be a save against your spell save DC. Also, you can't stone shape a petrified creature, because a petrified creature is not considered an object.

Okay thanks. I knew it was to OP to work. But what about Create or Destroy water? Create water in their lungs or destroy the water in their veins. It says create water in containers within range. Lungs could count right?

Quote from That_Poptart >>

If there is no specification, it's assumed to be a save against your spell save DC. Also, you can't stone shape a petrified creature, because a petrified creature is not considered an object.

 Your right the rules for petrifaction says that it's still a creature thanks!

You'd be hard pressed to find a DM who would ever allow you to use that justification to create water in someone's lungs, especially since the spell was obviously not meant to do that. 

But if you insist on an explanation...

For Create or Destroy Water, you can target a container to fill with water. A container can be defined as a receptacle meant for the storage of goods, which is obviously what the spell's creators were intending you'd target with it. Yes, lungs can contain air, but I don't imagine most people would keep another person's lungs around to hold their water like a fleshy water bottle. The same logic applies to destroying water in a person's blood vessels. And assuming that a person did count as a container for which you could store water in, it would make the term "container" so vague that it ceases to have useful meaning. If a person is a container, isn't every plant, crack in the sidewalk, and space of air between two solid objects a container? Just some stuff to think about.

So what happens if you try to target a warforged? I'm assuming your "attempt" fails?

Yes. Instead of saying "you target a creature" and leaving it there, it specifically says "if the target's body is made of flesh...."

So this would not work on a Warforged. 

I wish my 10th level wizard could cast this it would make his life so much easier

I just thought of the coolest application for this spell! So what is there was a wizard that acted as a plastic surgeon by completing this spell on people, using stone shape to do surgery, and then casting greater restoration to bring them back? Man I really need to start DMing again!

Quote from Gamesalami >>

I just thought of the coolest application for this spell! So what is there was a wizard that acted as a plastic surgeon by completing this spell on people, using stone shape to do surgery, and then casting greater restoration to bring them back? Man I really need to start DMing again!

 This isn't going to work because petrified creatures aren't objects, they are creatures with the petrified condition.

So what, if anything at all, can one do with a creature under this spell's effect that one couldn't do with a creature that's not?

We've ruled out Stone Shape, anybody have any more ideas?

Reading the petrified, I don't see anything that says a petrified creature doesn't need to breath. Would they die if tossed into a lake and they couldn't breath before? I know in Tomb of Annihilation:

Technically yes although I assume that's meant to be errata'd otherwise it'd be an instant death sentence since they're made of stone and can't breath on their own anyways.

Yeah, that makes sense. It would eliminate much of the mythic feel of petrification if it people could only survive a short time or would need outside help to live.

It´d be neat to turn a campaign villain into a statue then put them somewhere for the public to view.

My 5th level wizard just got a Bracelet of Rock Magic form a module. It allows him to cast this spell 3 times total (as in ever) using it.

My 5th level Wizard l, who just got 3rd level spell slots, has a magic item that lets him cast a 6th level spell. Yes it only can cast it 3 times ever, but it still seems insane for an early character.

The bracelet was in a trapped eagle head that bit down when touched, but I just used Mage Hand to grab it, so I was safe.

I had an idea about an ancient hero willing letting themselves be petrified as a form of suspended animation, to be awakened if the evil ever returns. They spend centuries enshrined inside a temple and most people just think they're a statue. It's up to the party to discover its secret and he gives them the secret to defeating the end boss.