Tip: 'Unique' means a passive does not stack, no matter how many you buy
So, I just wanted to point this out... I'm bronze, but still just had this happen. Went against a Syndra that was doing pretty well in lane, but by the end we were beating her a lot easier. End game I noticed this as her build:

Edit:
[{quoted}](name=Tidal Tyrant,realm=EUW,application-id=3ErqAdtq,discussion-id=4O5xA5Qq,comment-id=0000,timestamp=2016-10-25T16:23:17.251+0000)
Also, unique passives like Lifeline
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do not stack, despite being on different items :l
Edit 2: Greatly explained here:
[{quoted}](name=Inept Maverick,realm=NA,application-id=3ErqAdtq,discussion-id=4O5xA5Qq,comment-id=0003,timestamp=2016-10-25T18:20:52.989+0000)
To be crystal clear, this is how it works:
Passive: -------------------------
This means the Passive will stack in every way. Multiples of this Passive from the same item will stack and similar passives on different items will stack with this. Ex:
+
will grant 8 mana on unit kill.
UNIQUE Passive: ----------------------------
This means that buying the same item multiple times will not grant this Passive more than once/the Passive will not stack from the same item. However, the same UNIQUE Passive from a different item will stack. Ex:
+
will grant only +10% CDR, but
+
will grant +20% CDR.
UNIQUE Passive- Name: -----------------------------
Other UNIQUE Passives with the same name will not stack in any way what so ever. The only exceptions are Spellblade and Echo, which will use whichever effect is currently more powerful (still not stacking). Iceborn Gauntlet will stack with other Spellblade effects for example, but the AoE Damage will only damage the primary target if the other Spellblade effect would deal less damage. Ex:
+
will only grant one instance of the Rage passive. Dealing physical damage will proc Black Cleaver and basic attacking will proc Trinity Force, but performing a basic attack that deals physical damage will only proc one of the items.
do not stack, despite being on different items :l
+
+
will grant +20% CDR.
+
will only grant one instance of the Rage passive. Dealing physical damage will proc Black Cleaver and basic attacking will proc Trinity Force, but performing a basic attack that deals physical damage will only proc one of the items.

+
if they have a balanced team comp and you want to have 45% cdr.
and
stack with each other but not themselves.
share a counter, but ONLY proc when its applicable. shiv will only proc if youre within shiv range and RFC will only proc if youre outside shiv range.