So uh.. seriously.. MF is terrifying with the assassin item.. I STRONGLY feel like this is broken as all heck.
I had no warning to my own death.
Joseph Gladstone1 votesLOL
S0kaX1 votesLOL wtf was that damage?
Hige1 votesMF's double up does 50% increased damage if the first target dies for a maximum of 240 + 150% AD at lvl 5, in the video she probably has it on lvl 4 only which is 195 + 150% AD, given that she has around 200 AD the total damage would be 495, after resistances (41 armor as shown) the damage is reduced to 410
The bullet also applies Love tap which at lvl 7 (she's 8) does extra 70% AD the odd part is that in order for love tap to do 147 as shown in the video, it would have to ignore resistances O.o which isn't something love tap is supposed to do... kind of odd.
Last but not least, 
nightfall: 90 + 25% of the target missing HP, since Zilean had only like 25% health left, nightfall does crazy amounts of damage.
also take in account that if Soraka wouldn't have used her silence and done 58 damage, Zilean would have lived with 38 hp or so haha
k wìx1 votesWhat is needed is an indicator to the incoming bonus damage from Nightfall.
Hige3 votesO.o there is an indicator buddy, take a look at the red dots glowing on your character while you walk away... now as far as calculation all you need to know is that if you're below 50% you'll take a LOT of damage so you should be extra careful with it
edit: again, Soraka doing her thing lol, the text message saying you were silenced kind of gets in the way of the visual cue for nightfall