So what are people's thoughts on using this on a dead body with missing limbs, head, organs before using Raise Dead to restore someone to life? Would be easier to do than a wish spell but if you were a DM would you allow this or not and why?

I'd have the regenerate spell half revive it and make it continuously regenerate, and compliment on the one who cast the spell for creating a new kind of Undead.

Apologies for the necro reply but this requires you to cast it on a creature. Once someone is fully dead, they become an object. You can cast it on someone making death saving throws but once they are truly dead, only resurrection magic works on them. 

Quote from Jayne_of_Canton >>

Apologies for the necro reply but this requires you to cast it on a creature. Once someone is fully dead, they become an object. You can cast it on someone making death saving throws but once they are truly dead, only resurrection magic works on them. 

Dead creatures are still creatures. If they weren't, you wouldn't be able to use resurrection spells on them, because all resurrection spells reference "dead creatures" or "creatures who have died".

That said, dead creatures can't regain hit points, so the spell still won't bring them back to life. One could argue that it would still reassemble a corpse that had been cut into pieces, resulting in an intact (but still dead) creature. That seems contrary to the intent of the spell, though.

Sorry to say, but per the definition of an "Object" in the '24 PHB...

An object is a nonliving, distinct thing. Composite things, like buildings, comprise more than one object. See also “Breaking Objects.”

With this in mind, a corpse (which is no longer living) is considered an object. The spells that bring creatures back to life make the distinction of "dead creature", which is an exception to the normal rules for what a corpse is for that spell's purpose.

Quote from Someguythatplays >>

Sorry to say, but per the definition of an "Object" in the '24 PHB...

An object is a nonliving, distinct thing. Composite things, like buildings, comprise more than one object. See also “Breaking Objects.”

With this in mind, a corpse (which is no longer living) is considered an object. The spells that bring creatures back to life make the distinction of "dead creature", which is an exception to the normal rules for what a corpse is for that spell's purpose.

Whether it's an object or not is irrelevant; whether it's a creature is what's relevant, and again the fact that there are spells and other rules that refer to "dead creatures" mean that it's possible for something to be dead and still be a creature.

Maybe it's an object too — nothing says it can't be both — but that doesn't matter in this context.

Well RAW it wouldn't work, Regenerate targets a creature, a dead body is an object. As a GM I'd probably say no, my logic being Regenerate, and other healing spells turbo charge the body's natural healing ability, a dead body has no such ability. Its the same reason you can't cure wounds someone back to life after they've failed 3 death saves.

Quote from WhiteKnight416 >>

Well RAW it wouldn't work, Regenerate targets a creature, a dead body is an object. As a GM I'd probably say no, my logic being Regenerate, and other healing spells turbo charge the body's natural healing ability, a dead body has no such ability. Its the same reason you can't cure wounds someone back to life after they've failed 3 death saves.

If a dead body isn't a creature, then all of the spells that bring a dead creature back to life — Revivify, Reincarnate, Resurrection, True Resurrection — can never be used at all, because every single one of them says that it targets "a dead creature".

As I said above, whether a dead creature is an object or not is irrelevant; what's relevant is whether it's still a creature, and the use of the phrase "dead creature" in those spells' descriptions mean that it has to be, or those spells don't work as written.

Thanks for the replies above. To clarify the full reasoning in a bit more detail the rule for Raise Dead includes the line:
"This spell closes all mortal wounds, but it doesn’t restore missing body parts. If the creature is lacking body parts or organs integral for its survival—its head, for instance—the spell automatically fails."

Hence, I was wondering whether you could use Regenerate to regrow the parts of a body in even a dead condition to then subsequently use Raise Dead. As some have mentioned, a dead body would be considered an object as RAW but as Raise Dead could only be used on creatures that have not been dead for more than 10 days its not something that could be horribly abused and might be considered a creature for the purpose of the spell.

However, all of this might be kind of pointless as although this might be cheaper to cast than Wish, you could just cast Resurrection without the confusion of everything else and is also a 7th Level spell. If you are using spell components in your game then this might be an interesting alternative to finding 1000GP worth of diamonds for Resurrection.

RAW the above posters have all pointed out that it only works on creatures.

But as a DM I would absolutely allow you to blow your seventh level spell on something that is likely to have the same effect as mending on a corpse(or creature that once once alive)

My imagined scenario for you doing this is the DM used a vorpal sword on your ally and they're dead and have no head. You defeat the bad guy but at level 13 are still incredibly poor adventurers. You may be able to sell that schmucks sword but not for enough to bring back headless Alan. So you cast regeneration instead. Alan grows back his head and now can be rez'd on the cheap, and has a second head! Generally your going to have the missing body part nearby so mending won't be an issue but takes a minute so it excludes revivify, so does this.

 In general there's no reason to prepare raise dead or resurrection unless you know you've got to bring back alan, if he's dead today hell be dead tomorrow so you'll have to go back to camp, carrying him around until you get that sorted out

Wouldn't allow it on a pile of dust after disintegrate though, or any other effect that says something along the lines of only a wish spell can fix this. GOTTA let true resurrection shine.