Is there any chance for person lost in space and time to return?
Yes.
It sounds really weird, but it looks like, that only good working way of asassination for asassins is asassin summoning something better then himself to do the job.
No, but it's definitely the cheapest. Thugging out assassins or getting your hands (usually via shenanigans) on better-than-human ones are also pretty much perfectly workable, it's just that a simple skelliespam+acorn (or whatever) combo is probably going to do better than it 90% of the time. Doesn't mean the non-summoning option isn't good, just that the summoning method is faintly ridiculous
Do poisons stay after the battle ends?
No.
Any way to remotely horror mark someone without combat?
Blood magic has a few ways. Mostly by sending horrors (which mostly can horror mark with some of their attacks) to remote attack. Which still sorta' involve combat, but you don't actually have to have your mages there for it.
Is there anything capable of absorbing people for hp increasing like eater of dead?
Some pretenders can do the same thing.
There is horrific angel from hell, it has 25 nonmagical damage resistance( something like chance not to get damage at all thing), it is also ethereal because of some special robes to be even more pitchforkresistant, it has pendant of luck and flying shield and the shield in each hand to finish pitchforkproof kit. How peasants with pitchforks still kill him?
Fatigue + RNG, probably. Defensive methods are half-way to irrelevant if the critter isn't fatigue neutral -- eventually the fatigue will add up and the critter will die. SCs that aren't fatigue neutral pretty much have to rely on heavy offensive (probably on top of fear, or some equivalent effect) and just enough defense to survive, instead of heavy defense. Especially because you had two shields, the thing was likely just not doing any damage, got tired, and basically keeled over dead.
Also invulnerability is kinda' junky, from everything I've seen. Terribly unreliable, possibly even moreso than plain protection. Don't rely on it or expect anything from it, heh.
Do effects of two same items stack? For example two scutata volturna for double disintegrate per turn(+ lightening bolt shooting helmet c:) or double bane venom charms on harvester of sorrows
Generally they don't. Weapons are about the only exception, iirc. Not sure how stacked up shields work with regards to stuff like auto spell -- you'd definitely get the defensive bonuses, but not sure about the spells. Can test, quicklike...
E: Yeah, both shields would cast shocking grasp. You, uh. You would never want to actually do that, since you'd be pretty much guaranteed to get more benefit from one of the AoE one-handers or a different shield (gleaming gold, charcoal, vine, eye, whatever) instead of stacking them up, but... you could.
