Although in theory super psi like "Mentally Possess Others" could theoretically work, the limited duration could mean eventually you might have have a confused/angry god free and out for revenge.
Dark Conversions (Rifts CB3) has a couple indefinite takes though
107: Elemental Possession. This probably is not a viable option though. "lesser supernatural beings, humanoids, animals, or other life forms" in spirit is likely meant to imply that GREATER supernatural beings would be off limits (even if on a technicality a "humanoid" greater supernatural being might qualify)
188: Possession rules opens with "people or animals" so I'm not sure if this is meant to imply anything about supernatural creatures being off limits... these are rules which AFAIK are only used by Alien Intelligences (split essences) and the Possessing Entity from BTS (pg 82 of DC) though I'm probably forgetting some examples.
Pg 83 also specifies "human or animal" (wait, humans aren't in animal kingdom?) which I guess makes living plants and living rocks off limits (Biomancer Trees and Warlock Golems : celebrate) but raises the question: are elves/dwarves/orcs animals? Are gods?
This is especially important due to the expanded weaponization of Possessing Entities as of Splynn Dimensional Market, the "Entity Domination Staff" reprinted on page 257 of the Book of Magic
this opens their use to a wider population than the traditional Summoner/Shifter, mage who casts "Summon and Control Entities", or the "Ghost Makers" among the Noro in Rifts Dimension Book Two: Phase World.
BOM257 notably says "enables the user to mentally dominate anyone" and given this was written for an island setting full of a lot of things besides humans, that's a significant thing to write where I would not assume it just refers to "human or animal" like the traditional Possessing Entity writeup does.
I'm wondering if one thing that could help settle whether or not a category of creature is vulnerable to possession is to hunt out bonuses to save vs it for such creatures.
"Immune to Possession" might not be enough (it could just be reiterating something we're expected to know) but a BONUS implies you bother to roll at all: meaning it is possible to fail: meaning that category IS vulnerable to SOME kind of possession, even if it might not be clarified which type.
Pg 56 of Dragons and Gods for example gives a Minor Earth Elemental "+14 to save vs possession" which implies it is possible for something out there (AI? other elemental? possessing entity? dunno) to possess them. It'd be super-hard because even if the MEE rolls worst (1s) they get at least 15 which means the attacker needs to roll a 16-20 (25% chance at best) and I've never actually seen attackers EVER get any bonus to this roll, always seems to be an unmodified D20
+14 seems consistent for all the lesser elementals while "Impervious" is the policy for Major ones.
DG70's natural abilities don't mention alien intelligences have immunity to possession... although it might be kinda implied on pg 72's "impervious to further possession" that Essence Fragments give a physical body they inhabit. It'd be pretty strange if a mere fragment could make it's foreign body immune to possession while the original body with an unfragmented soul was somehow vulnerable to it.
Pg 73's "Cannot possess other supernatural beings" of course would prevent AIs from possessing each other, but there isn't any disclaimer like this I'm aware of for non-AIs with the power like the BTS-originating Possessive Entity.
If they WERE somehow vulnerable to this, pg 73's "+1D4 on all saving throws" would at least give some small resistance to it... plus I'm sure many of them would know magic spells to supplement that. It would be an interesting vulnerability though: might explain why some AIs are hesitant to leave their sanctums in case a roving Possessive Entity sent by an enemy hijacked their beautiful tentacled body.
Pg 89 of Dark Conversions does mention "Impervious to possession, even by other gods" under the Alien Intelligence template. There are differences between the DC/DG templates for AIs so you might have "Dark Intelligences" (rolled via CB3) which are always immune and "God Intelligences" (rolled via DG) which are possibly vulnerable, to make it interesting. I expect they just omitted it by mistake in D+G though.
Spirits of Light do not single out any bonus to save vs possession, but do have a bonus "on all other savings throws" which could apply to it if they were vulnerable.
I don't actually see "possession" singled out for any god either, though "on all savings throws" is very common. Unfortunately the OAST phrasing is of no help for setting precedents like a bonus SPECIFICALLY vs possession would be (like w/ Lesser Elementals)
Dragons have a similar "all other savings throws" (AOST) phrasing so I don't know where to find if dragons are vulnerable to possession either.
Some members of the Godling CC (who I believe are supernatural creatures: not sure if you would class them as "lesser" or "greater" though) are implied to be vulnerable to possession since pg 16 of Rifts Conversion Book 2 (Pantheons of the Megaverse) ability 7 (impervious to one type of attack) includes "possession" as one of the selectable options.
Elsewhere in Pantheons:
- pg 59 notes a Sowki (Ea) is "Impervious to mind control and any possession" which could be a special rule for him (being a Major Pact witch) since DC97 doesn't appear to mention Sowkis having any such immunity... yeah that's DC 172 "impervious to FURTHER possession"
pg 95 notes Jupiter (AI) is impervious to both
pg 127 notes Siva's cobras are impervious to both
pg 129 notes the "Techno-Wizard War Helmet" worn by Skanda makes the wearer impervious to both... now why would he need that?
pg 163 notes the Midgard Serpent is impervious to both
pg 169 notes Berserkes are impervious to possession while berserk
pg 178 notes Zurvan is impervious to mind control and possession
pg 179 notes Ahura Mazda is impervious to possession (no bonus vs mind control but he has decent magic/psi bonuses)
pg 181 has Asha immune to both
- 182's Vohu Manah lists no immunity to possession so in theory he should be vulnerable, yes?
- 184/185 notably does NOT list any immunity to possession for Sharevar and Haurvatat ... so they COULD be vulnerable to it... no bonus to save!
The contrast of the Persian Pantheon is probably the most intersting thing about Pantheons, where reading closely has 5 who are explicitly immune to possession and 3 who mention no such immunity.
The 2nd most interesting being how Skanda of the Indian Pantheon wears something conferring possession immunity, implying he might need that.
3rd being how Midgar Serpent is the only entity among the norse (aside from Berserkers) who mentions this.
All the other gods presumably have no such immunity (or even a bonus at all) which could make them super-vulnerable to being spammed by a dozen Possessing Entities sent by an enemy Shifter/Summoner.
Which would mean they would need countermeasures of some kind. I expect wearing a "Protection Against the Supernatural" amulet (BOM143: 12th level spell) would be popular for these guys. Or maybe more than one? It's only +2 so you might want ten of them if the bonuses stacked. It doesn't say anything about being unable to stack benefits of multiple copies of the same amulet, though I'm guessing that's probably implied somehow in the general policy of how spells operate (ie can't double-cast Armor of Ithan simultaneously) or in some FAQ.
Pg 122's "Magical Adrenal Rush" is one option but it doesn't last very long and has a bad come-down. I could see some gods maybe opting for this if they could make a longer-duration version (TTGD) or make it permanent (Rifts WB35 demon magic) in which case you'd only come off the high if hit by a Negate Magic or Anti-Magic Cloud.
Pg 124's Sorcerous Fury resembles Magical Adrenal Rush in that it's a way to get impervious to possession for a short period of time, but the exhaustion after it ends would make it undesirable for a lot of gods, and more an option if you're going to do a permanent version. The "will only want to hurt and destroy" would make a permanent-BAT undesirable for most good gods I would imagine, but I could see a lot of evil gods like Yin-Sloth being okay with that.
- pg 154 "Blood and Thunder" version of casting this on a group of people mentions that it won't work on Supernatural Beings but I don't see this mentioned for self-casting Sorcerous Fury
Pg 130's Protection Circle: Simple doesn't give immunity (or even a bonus) vs possession, but it does keep lesser supernaturals like entities and lesser demons like ??? away, eliminating a lot of the "casually spammed possession" threats a god might face. You could have a god send out minions to make these circles to "prepare an area for my arrival" for a mere 45 PPE and then only 4 PPE per 24 hours to activate could allow many circles active casually.
Pg 144's "Ensorcel" would be a more absolute defense since it makes you impervious to possession. This makes me wonder if a god could "Ensorcel themself" to give themselves that immunity (plus immunity to illusions and mind control and +4 vs all magic) without the usual drawback of worrying about no save vs the sorcerer who ensorcelled you: that's probably a good thing so you don't need to roll a savings throw against any magic spells you want to use on yourself.
Pg 148 (Protection Circle Superior) also gives impervious to possession, so gods who lack this as a natural ability might habitually only opt to inhabit activated superior circles to guard against roaming entities. Of course "supernatural beings" (which I think includes all gods) can't come within 20ft of the edge of these, so using the lesser variant to allow more inter-circle mobility by the god could be better: a god who steps inside a PCS is basically trapping themself against walking out, they either need to deactivate the circle or teleport/portal out to escape.
Pg 175 "Bee's Wax Effigy" can give imperviousness so I imagine some of the Russian Gods left out of Mystic Russia (stats in one of the canon Rifter articles) could make use of this. Haven't checked if they have possession immunity or not. Maybe other gods if they learn about these effigies will go barter with russian mages to get them cast?
- Huh... if you could make that permanent and then stack it, a bunch of +6s to PS could really add up... which FAQ had that anti-stacking prohibition on spell effects again?
Pg 192 has the necro spell "Death Wish" and I could see some war gods being willing to consent to this being put on them. No fear of death and suicidal tendencies is probably something many demon lords wouldn't want to risk, even though the possession bonus could help them avoid losing bodily control in that situation they could be at more risk from other dangers.
Pg 280 has the Black Hellebore tea which a god might obtain vials of as a means of getting a possession bonus in situations where he/she must venture beyond the boundaries of protection circles they might sleep behind...
Pg 281's magical three-leaf clover might be something all gods would want: it mentions being impervious to possession, although in this context I'm not sure if it means ALL possession or merely "possession .. by a witch". I'm thinking ALL because pg 283's overview only says "impervious" without specifying witches.
pg 310 has an inuit amulet (raven bones/feathers) which grants imperviousness so if a god ever heard about this they might want to try and get one. Angakoq has to bestow it though, so you'd probably have to help out people and be perceived as a nice guy for them to give that sort of gift.
The cool thing about these items is while it prevents "I win by spamming god with entities" brute-force victories, it has this RP element of something you might steal from a god to make them vulnerable to such an exploit. You could be sent on a quest to steal Thor's clover charm, for example, so that a shifter can try to have his entity possess Thor and use him to attack the Coalition States. You might even be a sorta good guy and not know the ramifications of stealing the clover: it's just a clover right? Maybe you got told Thor stole it, or the clover is being used to curse Thor so you're actually helping Thor by stealing his magic clover.
Elsewhere in Dark Conversions:
[list=]pg 26 Belphegor is "impervious to poison, drugs, gasses, possession and Horror Factor." (no such immunities are mentioned on pg 25 for Abrasax and pg 27 for Modeus only says "impervious
to poisons/toxins/drugs")
- Modeus has a "+3 on all other savings throws" while Abrasax has a "+2 on all savings throws" so if they're not immune like Belphegor explicitly is, it would still be slightly harder than possessing a human
pg 40 Mephisto is "impervious to Horror Factor and possession,"[/list]
If Sahtalus/Mephisto are impevious but Modeus and co (Belphegor seemingly the only explicit exception among Demon Lords) are not, that could explain why demons might be on such a defensive despite having game-breaking benefits like Demon Knights at their disposal. They would probably, if they wanted to intervene, want to do that via an alternate body while keeping their bodies protected, whereas Saht/Meph could occasionally jump into combat directly if it were beneficial, since a roaming possessing entity couldn't compromise them.
Thin Ones (DC 40-43) are a new "indefinite possession" option. I'm not noticing any prohibitions about targets (am I missing something like "no possessing greater supernatural" ?) although it sounds like their standard tactic (touch equivalent to the Paralysis Bolt spell) could face problems against targets with a high save vs magic (presumably you get a save throw) such as gods/AIs tend to have. I don't see any combat rules on how they might go about trying to crawl in the mouth of a creature they were unable to paralyze, like they might need to do if there was an anti-magic cloud or a person impervious to magic like those Magebane guys in the Merc supplement.
The Winter Storm Ice Demon (DC43-44) is explicitly imperivous to possession under their "Bonuses", which we don't see for the Thin One (so I guess an AI fragment could possess a Thin One who is possessing a supernatural being, working around their usual prohibiiton against possessing fellow SNBs?)
Boschala (DC72-3) get a +3 vs possession and I know they're lesser SNBs so you can clearly possess lesser SNBs at least...
...prior to this the Banshee (69-70) mentions no special bonuses, so I guess in theory you could mentally/spiritually possess an incorporeal ghost demon?
Darota (73-4) don't give any bonus whatsoever, so I would figure they're more vulnerable than Boschaal to possession...
Goqua despite being great SNBs go out of the way to specify being immune to possession (DC90) as do Mindolar (95) while the Death Weaver (98) gets a +5 bonus (BTS1p154 classifies them as Lesser though, not Greater)
Nightlords are impervious... Night Princes are +9...
Demonlings +6 ... Red Flame Demon Lords impervious...
One gets sort of a sense that "Lords" (usually on par with gods) are probably meant to be impervious all-around even if it doesn't state that...
Though I do like the idea of Red Flame Demon Lords / Nightlords having this neat advantage over the "greater" demon lords of Hades of being non-threatened by possession while the "more powerful guys" are actually vulnerable to it: it would explain why they take a more active hand in affairs while the other guys tend to lurk in their fortresses using walls of minions to guard against roaming Possessive Entities and AI fragments.
I expect in their millenia of existence, Demon Lords have probably heard about countermeasures like a Mystic Herbology's Magic Three-Leaf Clover (assuming they haven't just permanently cast Ensorcel on themselves, which sounds like a smart thing to do if you're capable of it and willing to burn sentient souls to accomplish it) and stack up lots of these countermeasures to compensate for any lack of immunity to possession they have, along with lurking behind protection circles in their sanctums.
One big hole in all of this is of course all of these countermeasures are MAGIC, so the protection they provide could be neutralized by an Anti-Magic Cloud, so these guys would be pretty scared of anti-magic clouds being cast by outside parties and run away from them even if they're strong enough that they don't rely on magic to inflict or protect themselves from damage.
I think if you preemptive cast Anti-Magic Cloud (which doesn't effect you) it could interfere with other people casting an Anti-Magic Cloud (not entirely sure how to game that out) so one other countermeasure might be to have a permanent anti-magic cloud up to protect you against that.
I don't know how AMCs effect magic items you wear though... like does it only ignore spells you personally cast yourself? That would create a problem if you relied on other people to make the objects for you.