Randuin's Omen

Anyone care on elaborating on the +0.5 seconds for each 100 Armor and Magic Resist? Does that mean the user or the effected enemies' resistances?

so say I get 100 armor and 99 mr. Do I still get the .5? Do I get 1 second additional if i have both 100 armor and magic resist?

I don't care about my rep, but you can +rep if you want to.

That is correct Keels.
At 99 armor and 99 magic resist, you get no bonus seconds.
At 100 armor and 99 magic resist, you get 0.5 bonus seconds.
At 100 armor and 100 magic resist, you get 1 bonus second.

Is this Item worth it even w/o the active?? When I get this Item I usually 4get to use that Active! Nevertheless, this item is just an overall awesome tank item (: ..

It is worth it even without the active, the passive and the stat bonuses are insane.

i like how it has a chance to slow attackers not the defender like most items

I like use this on tanks who have a "taunt" skill, or on duelist to make me have advantage 1vs1

Does anyone know how the mechanics work with stacking, in other words, how it is computed relative to the enemy's attack speed?

For instance, take Lee Sin's Tempest/Cripple and apply it, then using Randuin's Omen's Active, does that reduce by 35% of their current movement/attack speed after Cripple, or is it another 35% reduction off their base speeds, stacking for an effective 95% if proc'd together.

In the first case, would it then be more effective to use Randuin's before applying cripple?

Randuin's Omen+Force of Nature+Warmgog's Armor=U can't die!!
Awesome item!