I think Executioner's Calling could be better if it had a second upgrade into a more powerful item.
Tentative name: Headsman's Guillotine.
Total cost: around 3000 gold.
Stats:
-45 AD
-20% attack speed
-20% crit chance (like Executioner's calling)
-Unique passive: Grevious wounds for 1.5 seconds on-hit (like Executioner's calling)
-Unique passive: Basic attacks deal 8% of the target's MISSING health as physical damage.
(all numbers are tentative and subject to heavy change, they are all just placeholders the only thing I wanted to have is a % missing health on-hit damage item).
I think it would be awesome to have an item that does % missing health damage, kind of like the reverse of Botrk. It would fit very well with the theme of ''executioner'' and ''guillotine'' (% missing health damage is kind of like an execute). Another possibility would be to scrap the passive and instead give it an active that does 20% of missing health as physical damage and if it kills the enemy it gives your champion a moderate movement speed boost for a short time.