Trinity Force was only put into squishy AD heavy because if they are SQUISHY and are AD, they will most likely have gap closers to get to you, and you will need to delete them quickly, which is why i like the Sheen proc so much plus you get the Phage movement speed bonus to kite them. In a way, the survival rate Trinity Force gives you can be considered a defensive item. Of course if you are behind and you can't afford Trinity Force, you can also go Statikk Shiv into Phage (I will add this in)

Essence Reaver is the item I get when I don't need any other 6th item. If the enemy team doesn't 100-0 you, you will sustain back to full health in no time with the combination of Bloodthirster plus you get 80 AD

Maw of Malmortius I think plays a great role when you don't really need QSS, but somebody like LeBlanc is trying to come in and delete you in one go. Banshee's Veil is widely considered better, but I have explained my reasons in the guide as to why I don't usually take that item. Of course you can get MoM and QSS in the same build if you don't need Last Whisper though.

My build paths are somewhat unconventional, but this is what helped me climb through a lot of the ladder with just this champion.

But building IE followed by Triforce isn't a great combination because you're spending way too much gold into two main items of customarily seperated builds. If playing against squishy teams you will probably build the SAME items as usual like I stated before except for maybe delaying LW or building a needed defensive item earlier as usual. MoM, Triforce and ER aren't great items at all on MF, tbh.

@emoriam Thanks for being the first comment :)
Me not putting boots in was a silly mistake, I forgot to add them in. However, Squishy AD heavy and Squishy AP heavy are team comps that are full of assassins and have no tanks. Examples are as follows: AD: Riven top Zed mid Tryndamere jungle Corki ad Karma support. In this comp, nobody is really going to build tanky, with the exception of riven building a banshee's veil or randuins for a last item. Due to Miss Fortune's low survival ability, I decided to take out Last Whisper for items that grant damage + utility, which is Mercurial Scimitar and Trinity Force or Essence Reaver if they have no stuns/slows that will get you every time.

What I'm saying is, if they are squishy, remove LW and buy a different item(QSS like you mentioned) that will help you survive.

Youmuu's Ghostblade Is a preferential pick. I put it in the behind section because you can buy the 2 longswords as opposed to a pickaxe if you don't have 875 gold on your first back. Later on after Infinity Edge you can finish the 2 longswords into the blade. I simply don't like ghostblade, and I have created a new section explaining this item and my views on it.

I fixed my skill sequence, thank you for you feedback!

A few errors concering items: Do the folders "Squishy AP heavy" and "Squishy AD heavy" display example builds just without boots in the first place? Because I feel builds on AD Carries aren't changing against different kind of opponents except for the defensive items and penetration items. If enemies are delaying to buy resistances you can often ditch LW and buy it later on and against matchups like Zed or Lissandra an early QSS is needed, a.s.o.
YG is an item to purchase when being ahead rather than behind
Your skill sequence is messed! Your aren't putting three points in Bullet Time and six points in Double Up.