Dread Necromancer trick - need an explanation

[Theomniadept]

The following trick appeared in the Dread Necromancer handbook:

Magic Jar + Undead minion = +6 HP/HD to +infinite HP/HD: Use Magic Jar on one of your minions. Your body is "lifeless". This means you can animate your own corpse (assuming Lifeless = Dead, for all practical purpopses), and if you have a deadwalker's ring and corpsecrafting feats you just gave your body and extra 6 HP/HD and +4 Str/Dex. Its unnamed, so cancel the spell: you keep your body w/ the extra HP, Str/Dex. Do it again: you get another 6 HP/HD. And again. Its stupid. The only problem is that you can't apply the zombie/skeleton template on an undead creature, so you need a way to become "living" again, either by resurrection or some-such (Thought Bottle comes to mind). If you have the other corpsecrafting feats, apply those attributes as well: the bonuses only check when the undead is created, not after. Best reason NOT to be a Necropolitan at the start.

Can someone explain to me step-by-step how this works? I have never played a necromancer before and the guy playing the DN in our game will want to at least do this once.

[OldTrees1]

1) It doesn't work.

1A) Magic Jar only lets you assume the hp of a body while it is the target of the Magic Jar spell. At the end of the process you will ping pong back into your own body but will use your own hp not the hp of the infinite zombies you animated your body as.
1B) Bonuses from the same source do not stack. Each zombie will have only +6hp/HD. (Also see 1A, the 1st zombie will ping pong back to your/its body with its own hp, not the hp of the 2nd zombie)

2) It is problematic. Your body now contains your life force and an infinite number of zombie life forces. The DM should be able to figure out some negative consequences of being outnumbered infinity to one over what your limbs should be doing.

[Theomniadept]

See, you say it doesn't work, and I am one to assume infinite power is unobtainable except through he who shall not be named. But, for what reason does it not work mechanically? A bunch of unintelligent undead life forces in your body may be a little uncomfortable but unless otherwise stated it may be legitimate.

[Biffoniacus_Furiou]

A dead body is an object, if your dead body is no longer an object, i.e. if it becomes a creature, then it is no longer an object and no longer qualifies as being 'your dead body' as it is no longer a dead body. Even if that undead creature is then destroyed, it's now the undead creature's dead body, and not yours.

Even if it did work, on animating your body it loses all hit dice from class level, and becomes a 2 HD zombie. "The body retains its Strength, Dexterity, Constitution, hit points," you would only have 2d12+12 HP when you return to your body, regardless of your character level. Repeating the trick will only give you a better chance of rolling higher on that 2d12, it's not a way of gaining infinite HP.

Unnamed bonuses stack, but multiple unnamed bonuses from the same source do not stack. A given body can only benefit from the +2 HP per HD of Corpsecrafter once, it can only benefit form the +2 HP per HD of Desecrate once, and it can only benefit from the +2 HP per HD from Undead Mastery once. Trying to apply those same bonuses from those same effects multiple times will not stack. The bonuses to Str and Dex from both Corpsecrafter and Undead Mastery are specifically Enhancement bonuses. A Zombie gets Str +2 and Dex -2, but again multiple unnamed bonuses or penalties from the same source do not stack by default, so those ability adjustments from the Zombie template can only be applied to a given body once.

This trick does not work, and even if it did work, it doesn't work in any sort of beneficial way.

[Segev]

The point of failure mechanically is that your body is "lifeless," it is not "dead."

It is not a corpse.

You can only target corpses with your animation spells. It is ambiguous, but your body either counts as "a creature" (you) or as "an object." If the latter, you can use Animate Objects on it, but not Animate Dead.

[Theomniadept]

That kind of RAW would neeeeeevvveeeeerrr work. Convincing any sane DM that making your body lifeless doesn't make you dead would take some actual bribing with cash. But now I understand exactly where the trick halfway made it. Thanks for the info.