if you fail your charisma roll after the body dies you die.

Quote from Mannimarco_lord_of_evil_kittens >>

True you are not immortal in the traditional sense but if you are smart about it you can attain a form of pseodo-immortality.

for example if a wizard somehow manages to get enough gold and resources to produce or procure enough young bodies through the clone spell or kidnapping they could theoretically posess new body after new body for basically forever.

The only downside is that you somehow need to keep your original body alive but this can be achieved through the Imprisonment spell as well as somehow managing to maintain a constant supply of fresh young bodies.

Canonnicaly in dnd the ritual for lichdom requires you to make a phylactery(magic jar, Imprisonment, and I think soul cage), then die. That's about it aside from flavor text. No clue what sourcebook or edition that was for but the spells align to make it so. Finding that ritual in game is the tough part. 

i thought "ring of winter" + this spell = perfect preservation of old self while puppeteering new body.

Quote from metalphoenix22 >>

Far from it. You are not immortal and a simple spellcast of protection from good and evil will most likely just end up killing you.

 Not sure if anyones already said it but that only prevents possession, so it can’t just end a possession. It would give advantage on saves to get unposessed, exept the spell has no saves after they’ve been possessed. 

pretty sure you can also use this spell also using instant summons. allowing you to keep the container inside a bag of holding and have someone use it to retrieve you if the body your in dies. you'd need a way to alert when to use the instant summons for ally but should be an effective risk free way to scout

Hit points are part of Class features, your new body is you with new strength, dex, con and any additional feature as long as it's not a class feature. you get its hp and yours.

Allrighty, 

1. Start as a wizard, get to level 20

2. finger of death to make a zombie slave, true polymorph it into a griffon baby

3. Let that baby grow to an adult griffon, then true polymorph it into any dragon wyrmling you like, which can change shape, maybe twice to get the higher cr ones.

4. whenever you want, after it can change shape, have it become a humanoid, cast magic jar and tell it to fail the save. 

5. You are now in the body of whatever dragon form you want.

6. Secure the jar and your body, and profit.

ngl I'm just wondering how this'd work on a lich. like do you cast it on the lich itself or the phylactary? do you gain the lich's phylactary if successful or just the body of the lich? and if it did work can you then pull the ultimate poetic irony by feeding the lich's soul to its phylactary thats now your phylactary?

Quote from glasslad >>

ngl I'm just wondering how this'd work on a lich. like do you cast it on the lich itself or the phylactary? do you gain the lich's phylactary if successful or just the body of the lich? and if it did work can you then pull the ultimate poetic irony by feeding the lich's soul to its phylactary thats now your phylactary?

 This wouldn't work on a lich because their type is undead, not humanoid.

So... what about the targets memories/knowledge? Do you get that? Like if you possess someone do you get to know their plan? If they know a secret code/password, do you know it now? Is the mind tied to the body or the soul in DnD?

Boy!

You could use clone to keep a backup body to deal with the high chance of death from this spell

So about the wording in this spell. ”If your body is more than 100 feet away from you or if your body is dead when you attempt to return to it, you die.” but if your body is dead doesn’t that mean you could just NOT decide to return to it and instead just exist as a disembodied soul for as long as the container remains unbroken? And potentially possess anyone who comes within 100 feet of the container? 

Magic Jar into a humanoid

True Poly your original body into  an adult dragon - concentrate for an hour till it becomes permanent

End Magic Jar and take back over your now permanent dragon body?

Can somebody tell me how to calculate the HP officially ?

Lets take the Githyanki Supreme Commander for example. 

HP of the Gith: 187 (22d8 + 88)

Lets assume the Wizard is Level 12 (Con bonus doesnt matter i guess ?).

So some people say the calculation would be : 187 + 6+11d6 + 12x (New)Con Bonus (+4 from the Gith) = 187 + 6 + 11d6 + 48

Is this the official and right way to calculate it ?

Could you use an iron flask for this? It certainly would cost enough and being magical it would be much harder to break

you could if you used a true polymorph spell on it and turned it into a peasant or villager or something along those lines

If you have access to the Clone spell this entire process is moot, as Clone allows you to make a younger version of yourself for your soul to inhabit over and over again.

No, I meant for the spell component:

* - (a gem, crystal, reliquary, or some other ornamental container worth at least 500 gp)

 * posseses tarrasqe *.   Dm “ ohhh nooooooooo “