I am thinking of a build to make an (almost) invulnerable adventurer.
Basic tool for that is the use of bone shields. It is great talent, sustained and without time limits that auto regens every 5 turns and is able to block up to 6 attacks. The main problem with it is that many attacks with a small damage can completely ruin the shields in a couple of turns (DOT effects, terrain effects, melee project, been surrounded by many critters, etc). So the idea is to couple a bone shield with some mechanisms to completely suppress small damage attacks and let the bone shield act for high damage attacks, that are not so frequent and will give it sometime to regenerate.
One solution would be to use block and the spectral shield talent, that would insure that no attack below say 200 HP would reach the bone shield. A simple corruptor with a bone shield, a short staff, a shield and the spectral shield prodigy should already be extremely resilient, even more with the eternal guard prodigy. I am surprised not to have found any in the character vault. But the problem with block is that the protection is not permanent and we can do much better with an adventurer and some specific items.
To do that, first, have a look at the damage application mecanism.
According to the source code, the steps are the following (I think):
1/ apply premonition to define a % damage reduction
2/ apply block from shields to get a raw damage reduction
3/ apply forge_shield for a raw reduction
4/ apply psionic shields (kinetic, thermal, etc) for 50% reduction
5/ (apply damage smearing)
6/ apply resistances (for mob types and for damage types)
7/ apply antimagic field
8/ apply energy decomposition (30% reduction for any damage but phys and mind)
9/ apply flat_damage_reduction (raw damage reduction)
10/ apply prodigy roll with it (raw damage reduction for phys damage)
/11 Apply retribution (50% dam reduction)
/12 Apply displace damage (probability to displace 50% damage)
/13 apply sharing with bloated oozes
/14 Apply time_shield (sent forward in time)
/15 apply damage shield to absorb damage
/16 Apply displacement shield (probaility to send damage to foe)
/17 Apply disruption_shield to convert damage to mana
/18 Apply bone shield if some damage remains
/19 Apply the deflection talent to dismiss damage with your force of will
/20 Apply solipsism dismissal
/21 Apply feedback effects
/22 Apply Resonnance field
/23 Do the soplipsism conversion
For melee attack the process is basically the same:
/1 Deflect damage with gesture of wardring
/2 Suppress some damage with armor
/3 Apply the damage (see above)
So how to suppress small damages to preserve the bone shield ?
Effects applied after the bone_shield used are obviously useless in that case (deflection, resonnance, dismissal).
After step 10, the only raw damage reductions are damage shield, disruption shields and displacement shields. All can crumble and displacement is probabilistic. So they cannot be use for the basic mechanism, but can be a good complement.
Other effects (11-13) just reduce the damage but do not suppress it.
Roll with it could be great, but it only concerns physical damage.
Some talents are obviously to avoid. Antimagic field, for instance, while potentially a good candidate, would forbid the use any vim based activated talent (otherwise the eq will grow dramatically and the AM shield will crumble rapidly).
Forge shield reduction is quite low and at the really start of the process and probably not so useful in that case.
The best candidate to suppress damage is flat_damage reduction. This is only provided by few items (unfortunately no talent AFAIK), but can be very powerful. The items that provide it are:
* the mummy set (10 HP with the Crown, 30 when the set is complete along with great other benefits)
* the eternity counter (10 HP in defensive version)
* the Temporal Rift shield (20 HP)
The Rift shield can also provide Block, and is an excellent candidate for this build. So, we will assume that we get it and the mummy set (this assuption is obviously the most constraining hypothesis of the built, but the item vault can be used...).
It should be completed with Absorption to set up a psionic shield. Kinetic and thermal should be sufficient, with absorption mastery maxed, and we can reduce all damage, but lightning, blight, darkness and mind by approximately 50%. The damage cap of this talent is not a problem, as we try to suppress small damage attacks. More, having a focused weapon is always useful.
Also unlock Energy to get Energy Decomposition.
If we assume that we have 30% resistance (which is quite easy to get), we have a 0.5*0.7*0.7=0.25 damage reduction with the 50% of Absorption and the 30% of Energy decomposition. This way, if we have a 50 HP flat reduction, any attack below 200 will be just ignored and not transmitted to the bone shield. Is should sufficient to ignore all DOT damage (burning, terrain effect, wretchling acid, poison and disease (but the mummy set already give immunity), etc), melee projections, and melee attacks by the weaker critters. If the damage is not covered by one of the psionic shields, only attack below 100 will be suppressed. If the damage is not covered by the decomposition, the threshold will be around 150 HP. In either case, this protection can be completed by a shield block that with the spectral shield will add at least 200 to this value and remove any attack below 400. This should be sufficient to ignore melee attacks by most mobs, but elite and uniques, even in the late game.
Probably, with just that in the late game, you can stay at full health for maybe at least 30 turns during a fight, which should be sufficient in most situations, even with limited offensive possibilities.
After that, you still have many categories to use. Suggestions are
Conveyance for displacement shield ( step16). It is random but may reduce 50% of the use the bone shield (and approximately double its durability).
Disruption shield (step 17) can filter out most of the remaining. Maybe a bit overkill (overprotect more preciseley) and the aether avatar is a bit constraining.
Time shield duration is very short, but why not...
Of course set up damage shields from time to time to let the bone shield regenerate.
Celestial guardian is probably a good idea, as you already have a shield and retribution (step 11) can further reduce non ignored damage.
Armour can help to reduce melee damage. Maybe earth...
After that, probably aegis and light (otherwise, as the mummy set turns you to an undead, you have no way to heal and one never knows...). And some offensive talents.
I haven't tested, but it should would work as espected. A ghoul reaver with just the mummy set and eternity counter is already quite resilient, but without preliminary damage reduction the bone shield tends to crumble after some turns in the late game because of DOT and critter attaks.