Been trying to test her W on everything I can since I thought it could block anything but maybe I am missing the timing on it? Mainly, can it block those mid assassins ults, such as Zed, Talon and Kat? How about Cass' ult? Is there a comprehensive list? Or maybe it is shorter/easier to list what it cannot block?
Sona Ping4 votesThe Comprehensive List of Things Fiora Can Parry Because She is Just That Badass:
Mr Broken Wings2 votesit can block everything, even ignite or exhaust if timed right.
LaughingMan112 votesEverything that isnt a tower*
Persevence1 votesOk let's ee what you have. I would recommend checking out guides on FIora. Some people got more information about it. FOr example, you can look at a sivir guide for spell shield blocks.
What I have seen is this, you can block any stun. For example, I went against riven and blocked the w, this works for Irelia's stun too. I mentioned stuns then now the spells. Lux's binding can be blocked, Yasuo's tornado can be blocked, if Lux's q can be blocked then Morgana's dark blinding must also work. I just want to know whether you can block Malphite's unstoppable force. Can you test that out? To answer your question, Zed's ultimate is almost almost slightly to Lissandra's ice tomb. MAybe, not sure, but it is single targeted ability right? Maybe you can block Lissandra's?
ModWulf Helhammer1 votesEverything but tower shots. For things that happen instantly, it's more so a matter of you just being lucky (you can parry ignite and exhaust for example, but there is absolutely no way to predict them)
CrazedPorcupine1 votesIt blocks everything. Literally everything that touches Fiora during the .75 seconds that her W is up, Fiora is immune to. This includes summoner spells.
ModWulf Helhammer1 votesIt doesn't block turret shots
CrazedPorcupine1 votesNothing but untargetability and invulnerable will block tower shots
Vistha Kai1 votes
MunchCrunchLunch1 voteseverything but turret shots.
Renascent1 votesJust like everybody says, her W blocks everything that affects her.
Don't forget that it does NOT stop champions that rely on hitting a champion to attain certain effects that affect themselves (i.e. Darius Q heal).
Akasuisei1 votesSo to block Zed's Ult, would I have to use Q as he applies it or after its been applied but right before it does that last bit of damage?
Mirage Seraph1 votesYou can do either. Parrying during Zed's channel will block the mark from being applied, parrying when the mark pops will negate the damage. I would recommend parrying the initial mark since that'll also allow you maybe dodge the first couple spells he throws out.
trash sion1 votesEverything.
DeloricVI1 votesEverything that isn't a turret shot. As long as the timing is correct, she is 110% invincible while parrying. Some attacks' timings may be wonky though, but as it has been said, you can even parry summoner spells.
Stephenizgod1 votesThe only thing it can't block is Turrets.
Ruin Lance1 votesliterally anything that isn't a tower.
The Sword Saint1 votesIt blocks everything but tower/fountain.
Sneakyy XD1 votesTo those saying it blocks everything, are you sure? Does it truly block ground-based pools of damage abilities like Vlad's and Morg's W? Spell shields don't block those, and I would be surprised if Fiora's W does.
Z Statistic1 votesFiora poises to strike in the target direction and then enters a defensive stance, parrying all incoming non-turret damage and hostile crowd control effects for the next 0.75 seconds.
It blocks everything.
Daxanater1 votesa fucking mountain 
