Post your games!

Kinda of a odd thing tho, all the matches proceeding this had opposing marksmen using Runaan's and so did my team, and it became like a heated debate on it's usefulness.

It's a noob trap item. AD champions are the only ones with multiplicative scaling because mages can't crit. Attack speed is CDR for autoattacks. You wouldn't just get max CDR before getting damage, would you? You wouldn't buy an item that only gave CDR, would you?

*The downside to Shiv is that it's not as good on single-target DPS like PD is (so Shiv peaks in mid-game and then falls off late-game when single-target DPS > multi-target DPS as an ADC)

Edit: Reasoning behind Last Whisper being crucial as an ADC's third item (usually) is because this is around the time that tanks start building armor. Read its passive if you don't understand. Anyone who thinks LW is used for its AD did not read the power of its passive.

Shiv also has more movement speed, adds magic damage, and is wave clear. It's not as simple as "oh it falls off late game".

It's not just tanks building armour, built-in armour scaling also becomes a bigger factor at that point as well. I've been a long-standing proponent of increasing % pen on LW but only making it work on bonus armour like Yasuo's ult.