This will be a short one, this is just a notice to let Riot know that Yi's Alpha bug is still present where he would take damage and potentially die to attacks and spells during the animation even though he isn't supposed to due to invulnerability.
Please fix it, please, it's been way too long.
Modi1 votesYi is not invulnerable, yi is untargetable. Anything that is already targeted to him will still hit him. Things like AA projectiles (except Kalista), 
E, 
poison, 
Q poison, 
R when it hits you (you get the idea)
Master Yi teleports across the battlefield with blinding speed, dealing physical damage to multiple units in his path, while simultaneously becoming untargetable. Alpha Strike can critically strike and deals bonus physical damage to minions and monsters. Basic attacks reduce Alpha Strike's cooldown.
Master Yi teleports to strike up to 4 enemies, dealing 25/60/95/130/165 (+100% Attack Damage) physical damage, with an additional 75/100/125/150/175 damage to minions and monsters. During Alpha Strike Master Yi is untargetable. Alpha Strike can critically strike, dealing an additional 60% Attack Damage physical damage. Basic attacks lower the cooldown of Alpha Strike by 1 second.
SEKAI1 votesYi is not invulnerable, yi is untargetable. Anything that is already targeted to him will still hit him. Things like AA projectiles (except Kalista),
Except untargetable is for the most part, invulnerability in this game.
http://leagueoflegends.wikia.com/wiki/Untargetability
Untargetability refers to units in a state where targeted abilities such as Rammus' Puncturing Taunt and LeBlanc's Shatter Orb cannot be cast on the unit. Nontargeted spells such as Karthus' Requiem will also have no effect, an exception being Soraka's Wish. Additionally, they cannot be targeted by auto attacks.
Dashes Projectiles (basic attacks or abilities) that are mid-flight when the character starts dashing will hit when the dash completes. They still take damage over time while untargetable. Master Yi's Alpha Strike makes him untargetable for a short time while in flight.
Besides DoT, Yi shouldn't take damage and die to AoE and whatnot DURING Alpha Strike, which happens way more than I could count. It's clearly a bug not fixed.
Not to mention "Projectiles (basic attacks or abilities) that are mid-flight when the character starts dashing will hit when the dash completes" is bad design anyway. It's reeks of band-aid balance solutions, as it makes absolutely no sense to make a character, to take projectile damage AFTER it's already gone past them when the dash completes; it's like being stabbed by a flying knife that's already flied past and behind you, nonsense.
Modi1 votesIt is odd, but they would need to make everyone (and everything) like Kalista, in terms of projectiles. She is, at least I think she is, the only ranged champion that can miss an AA. That would be a significant power detriment for nearly every adc, to remove the existing mechanic.
I'm not saying it's a bad thing, but it would need to be compensated.
Thales2251 votesI cannot tell you how many times I've ulted a Yi as veigar and he alpha strikes me so he took no damage