I'm literally done with Assasin meta, playing as ADC when enemy mid is Zed/Diana/Yone, etc is exhausting. So I came back to the old days when Miss Fortune was killing you with autos. This build lets you battle: Assasins, Tanks, strong DMG ADC like Draven.

As an ADC try to stay on the back of your crew where you can observe when to strike. You are highly strong to survive because Immortal Shieldbow Passive and grants are great, but when they catch you and no one will help you to stay alive, you are screwed. Use your wards a lot, after the 9th level buy a blue one, and place them to be ahead of your opponent with vision, when they want to kill you, you would know. Try to enter teamfight as a 3rd person.

The one thing I can't stand on Miss Fortunes is how they farm. Jesus. Your Passive: is super strong. Try to use it as the most thing, switch targets while farming so you won't waste your mana, and do high damage to minions in a short time while pushing. You can easily use it to freeze farm also, just last hit minions with your passive! It's really not that hard. Use your mana wisely, try to always be about 50% of it at the lowest. If you are smart enough you will see that you can fast poke minions with your passive, and quickly strike your opponent with Q's when they don't expect it.

It's a super strong ability. I know Movement Speed and Attack Speed are not that impressive at first, but it can save your life. Use W to push, escape (when you are not anymore in range for damage - press W to escape faster until they shorten that range), fast regenerate HP/Poke (when you have a lot of lifesteal and then you use your W on different targets, the CD of it drops, so you can poke enemies, heal and escape at the same time, you can use it to chase as well.

Try to prock your PTA, use AA+Q+AA(high dmg), slow champions with your E, and get to them quickly with your W. Try to have W loaded passive before you engage so just in case you can escape with boosted MS. Use ult only in these two cases:
#1 - you can kill someone with it, and exclude his champion from TeamFight.
#2 There is a Teamfight, everyone keeps enemies busy so quickly find a position when you won't take damage/stun(you can for example dodge engage from the enemy and then quickly use ult on low targets), etc and use it.
You can of course use it on minions when the enemy is trying to dive you, but be careful, when you use it you are vulnerble and open to be attacked.

This Build gives you a different experience as a marksman. You are not that fragile anymore, you have Damage, a lot of HP, a shield, a booster to your life steal that is in the range of 35-50%, a way to kill and escape. In the late game, you can't be one-shot so easily so the assassins will struggle with you, you can buy time for your team or even kill while you've been surrounded. Fight till the end as a real Capitan.