You will first run into a tallboy at the very beginning of Mission 5: Lady Boyle’s Last Party. They are heavily armored soldiers on stilts that shoot incendiary crossbow bolts from very long range. The easiest way to kill one with your sword is to use Bend Time 2 and Blink—it can be done with level 1 but you need to be at a slight height advantage. When you use Bend Time 2 every attack during the duration is considered an assassination, so even blinking from the front will automatically kill it.
If you do not have Bend Time 2 you can also blink from behind while unseen, or use a Drop Assassination to kill it as well.
If the Tallboy receives damage from an outside source, such as a grenade or pistol shot from another guard, the trophy can glitch out and not reward you for the kill. Be sure that the target has taken no damage prior to you assassinating it.
To see a complete walkthrough of a Tallboy being killed with a sword, please view the video below:
I just used drop assassination on a tall boy. Was super easy.
Right after you are done at Lady Boyles party, there are some tall boys that roam around. Just blink up to the top of the street light pole, wait for the tall boy to roam underneath you, then drop ass on him!!
It doesnt have to be a drop...If they r unaware of u, u can blink straight up to them from the ground and assassinate them that way. It worked for me from behind and in front. But if u are slightly off with the placement of blink or the timing of the kill then u are in for a funtype fight. The last stage was loaded with them but i killed them all in one blink/strike each. It works and it really does look great polun1!!