if you agree thornmail is situational you shouldn't have it on your core build, I recommend changing it for frozen heart, and 2% damage with only 4 magic pen would be reduced to something around 1.6%, .8% on hit .8% over 10 seconds thats a total of 16 more damage over 10 seconds for someone with 1k of health, and by that point in game it's more likely that they will have less health than that, I agree you need the damage but boots are more important you need to at least get the 350g boots

i said that thorn mail was a situational item in the guide and i get blasting wand first so that his ult goes from 24dmg+0% of target's health to 2% for faster kills

buy boots of speed before blasting wand

thornmail is a situational item