ZEITGEIST [Spoilers] Possession in book #7

The Mortal Possession ritual/spell seems to be ripe for abuse after the adventure. It seems like a cheap way for a PC to swap their body into that of a high-Strength/Constitution/Dexterity NPC and then indefinitely run around with many of the benefits for having high physical ability scores. Intelligence/Wisdom-, Intelligence/Charisma-, and Wisdom/Charisma-based PCs all stand to gain plenty from possessing the corpse of a defeated antagonist.

Even if it could not be used on a corpse, morality may not be an issue for some characters who are supposed to be morally dubious anyway. It is fully possible for the vessel to be unable to affect the possessor's mind on anything but a natural 20 (in 4e) or a natural 1 (in Pathfinder). Meanwhile, the possessor is reaping many of the benefits of high physical ability scores.

How, then, is this supposed to be balanced for long-term use from book #8 onwards? It greatly rewards Intelligence/Wisdom-, Intelligence/Charisma-, and Wisdom/Charisma-based PCs who care little for their original body, while being far less appealing for PCs who actually invested in their physical ability scores.

Rules of magic are changed after adventure 9. If you see that your players are abusing this ritual, you can break it after that point. I guess the morality is supposed to be the greatest block here

First, ew, corpses? No, no, ew.

Second, it was intended to already be morally dubious whether it's okay to steal people's bodies when those people are villains and this is your only way to infiltrate. To casually possess someone's body for some sweet stat boosts is disgustingly evil. I mean, sure, let the players do it, but make sure they know they're the bad guys now. It's a pretty classic trope that being evil gets you power, but some hero will find out and stop you.

Third, if you expect min-maxers will do all this, and you don't want it to happen, you could just say that after the lich in the glacier provides knowledge of the ritual, you only get enough 'evil lich magic charges' to use it once per PC.

What exactly is the issue with using corpses for the ritual? It is not as though the PCs will not be killing bad guys from time to time, and it is not as though the ritual would cause the PC to be moving around in a corpse.

Honestly, I fail to see any suitable "bad guys to kill", which may interest PCs from the stat point and do not come with significant complications. Glancing through adventures 7-9:

• frost giants (Str 24, low Dex-Con) - problematic from the public viepoint, snow giant in RHC, hard to conceal
• Catarina Romana (Dex 19, not much) - actually may be interesting from story perspective, and gives Romana's spirit in adv 9 additional motivation
• Aulus Atticus (Str 20 Con 20) - gets the party in "exorcise on sight" Clergy list, no "ifs" or "buts".
• Betronga (Str 23 Dex 20 Con 17, innate regeneration) - possibly most OP candidate, but gives a lot of ways to affect character via lycantropy curse ("sorry, I just rolled 1, I get to control your PC this turn"). Also opens a way for some direct divine intervention from Hewanharinmau if you like that.
• Andrei von Recklinghausen - another OP variant, but undoubtedly evil. I think at least part of his Str 40 in stat block is caused by Nicodemus
• only Borebog and Copperhat seem to serve as suitable "evil guys" from adventure 9. Honestly I'd say their body dissolve into foul-smelling water and shatters into dozens of spiders upon death, respectively, they seem too "fairy" to exist on Material Plane anyway

I wonder how justified are your worries from this thread and the one before. Please post at least some initial impressions once you actually start the campaign. My own party included 2 players with a tendency to seek rule-breaking combinations. One of them eventually left the game due to unrelated circumstances, I still have the other (eladrin artificer with passive perception/insight 42 via Sorcerous Vision feat) playing, and so far the campaign held on quite nicely.

I have not had a look at your list for various reasons, but I am fairly sure that various nameless Obscurati mooks in encounters have decent Dexterity and Constitution scores for mental/mental characteers to hijack the corpses of.

We are already into book #7 and we are struggling with many of the mechanics of 4e and Zeitgeist even despite a 17,650-word (as of the time of this writing) document.

Oops, terribly sorry, confused you with another DM here. There seems to be a surge in 4e popularity recently

Mooks have Str-Dex-Con around 12-16 actually, best I can see is Dex 20, which can patch Reflex save of Wis/Cha based character, but not by much. But seriously, hijacking even a body of random hired gun seems like a thing that would raise a lot of eyebrows in RHC HQ and, probably, disapproval from Delft personally. If your party wants to minmax their chance to success by any means possible - that's not something you can "fix" with a patch of a single ritual. You can play on that, test if they are really ready to save the world but tarnish their name for all eternity, i.e. by offering "behind the curtains" deal with Nicodemus. Adventures mention the possibility of PC working for Obscurati, maybe your group is going this way.

If you're still looking for rigid mechanical limitations... NPCs in 4e only have one healing surge per tier. It would be quite hard to survive when you only have 2 surges per day (3 by epic tier), even with Comrades Succor ritual. Also, Mortal Possession ends within 3 rounds if the material focus is broken. I'd reason that "woven bracelet dipped in gold" can be disturbed by any area attack which deals 10 or more damage, so any hand grenade can lead to a very nasty surprise for PC.

What is there to say that the PCs would use the NPC's healing surges, any more than they would use the NPC's hit points?

I am still not seeing the source of objection to using a hired gun's corpse anyway. The PCs have likely been doing shadier things since much earlier into the adventure path, like making use of that Bond of Forced Faith ritual of supremely dubious origins.

Breaking the material focus with 10 points of AoE damage sounds as ridiculous as breaking all PC clothing with a similar amount of damage.