Hidden synergies and undocumented features! (Diablo 2)

Diablo II is very good, but very old game.
Game of the era when developed in the majority did not consider it necessary to explain to the players the intricacies of the gameplay mechanic. Plus a whole bunch of versions of make sometimes huge (here, managed to use =) changes.
The result was a vast array of nuances which sometimes do not even know the players with years of experience.
And okay if only they, even fan-made resources in your library do not contain this information!

To catch all these important things from the guides (often incorrect) forum disputes (in which the truth may be deceased) is exhausting and unproductive.
Therefore I propose to collect them here in this thread.
For clarity and accuracy, take the later version (>1.1), as the most popular and common.
Write what information you at the time, was surprised, puzzled, forced to re-examine and make changes in their own style of play, and I'll put it in the first message and available to execute.

So, I'll start myself:
Surely this is common knowledge, but for some reason neither the author guides neglected to mention this nuance, as the fact that synergy only give sub points. If you put one point into the skill, and then put things on a +20 to it, the effect of it for other skills will still remain at unity.
There are rare exceptions, consisting in synergy of the unique items that grant a fixed (aura LVL 16 for example) the ability and even skills, castelmassa with a chance (when hit, you get hit) but this is a bug and it works only on some versions. (on RuBattle - works) to Use it or not is up to your conscience.
(in the comments there are examples and a lot of, check out if you're interested)

Pumping auras on the paladin resists the elements (Resist Fire, Cold, Lightning) increases the maximum resistance to the corresponding element by 1 for 2 points invested. However, if you include the aura, the maximum resistance will increase by 1 for every point. That is: you pumped Resist Fire for twenty, put on a bunch of stuff on fire resist and your resistance is 85. But if you turn the aura, it will rise to 95.

The explosion of the corpses of the necromancer a very powerful spell... on pl1. More players greatly increases the health of the mobs (with 8 - 4.5 times), but for damage spells does the base value, without taking into account multiplayer modifier and a massive brawl efficiency suffers greatly.

The paladin takes damage while using necromantic skill Revive
(requires verification and details, to whom not in a breakage)

Potions of antidote and thawing not only remove the negative effects, but also gives +50 poison resistance (cold) and +10 to maximum poison resistance (cold) for 30 seconds.
The effect is cumulative, wygra drinking multiple servings, you for a few minutes get a high resistance that can greatly help out in the beginning of the game when you accumulate resists hard and endgame for cheap increasing their chances against the super-strong (uber) enemies that can cut your resists (including the maximum).
Important! Limit - no. Not at all. After spending some time (and money) from a dealer, you can nastuchat itself resists to cold and poison for a few hours real time. Until a reboot or death. Mortals, please note! For players on hardcore is just a gift from heaven.