Unique and not combinable items

Hello guys,
First of all, sorry for my bad english, as it is a foreign language for me.
I wanted to ask something to you: I am new to the game and I wanted to understand how does the "unique" items work. (I am talking about items like Mjollnir, Desolator and others).
So... in the description it says that those items can't be combined with other special attack modifiers, this means that if I buy an (I'll pick 2 random items) Eye of Skadi and then a Desolator, the Desolator won't work? (The armor penetration).
But let's talk about Mjollnir.... it says that it can be combined with other special attack modifiers... so if I buy the Desolator and the Mjollnir they will both work?
Thank you and regards!

I do believe that you cannot stack Desolator and eye of skadi]] together because they cancel each other... not quite sure about that. Anyway;
Other "unique attack modifiers" will stack with one another, a simple rule for some things, if it has a chance to activate then you can stack it with Eye of Skadi/ Desolator because it won't override it half the other time, only when it activates. Lifesteal can be used with all of them (pretty sure) and I am unsure about Diffusal Blade's mana burn. Anyway, simply, if it has a proc chance, it will stack with a perma effect such as Desolator or Eye of Skadi.

So to answer your question, Desolator and Mjollnir will both work when bought.

OK sooo this is going to sound complicated but ill try.

Mjollnir Maelstrom work with all UAM's but when the passive is proc'd it overrides the current UAM.

Vladimirs Offering doesnt works with some Ability UAM but not some Item UAM.

Mask of Madness works with some ability UAM but not others it definitely doest stack with Item UAM except the above.

Diffusal Blade Eye of Skadi Desolator do not work together the item that was most recently purchased provides the current UAM and the old one is replaced. stats and atives are still retained.

Items that are considered "unique attack modifiers" usually imbue your attacks with some sort of special ability. If you hit an enemy with a Desolator attack, that hit will apply the armor reduction debuff to the enemy unit.

Multiple UAMs (unique attack modifiers) cant be applied with simultaniously with an attack. Meaning that if you have both, an Eye of Skadi AND a Desolator only 1 of their debuffs will be applied.

However, there are some exceptions to this rule:

1. Mjolnir and Maelstrom have a %-based chance to proc (there is no guaranteed debuff) which means that attacks that acutally proc chain lightning override other modifiers...all other attacks can be buffed via other UAMs.

2. Eye of Skadi CAN be combined with lifesteal items. So using Eye of Skadi and Satanic will apply Lifesteal AND slow with EACH hit.

Also some heroes (like Drow Ranger or Viper) have built-in UAMs, so be extra carefull with itemization. Those spells are marked as UAMs in the tooltips.