I always thought they did that critical damage to duke, the big yellow damage markers are effective/crit damage but I've never seen them on the duke before, I've been okay with this as I've thought it was a bug but I need to know the truth here before I experience buyer's remorse.
Since you guys tend to know everything about weapons and damage values, I thought I'd post it here. I'm pretty sure this is the right place to post it as I'm asking for damage more than "why don't crits show up" but my friend has used the Volcanic Pepperbox on Vanaduke a lot, and he JUST got a plague needle so he knows that they will do the same damage at level 10, so this is actually a major problem because isn't vanaduke supposed to be weak to piercing?
Vanaduke is weak against piercing by a little bit, not by much. So you shouldn't worry.
Also, crit number appearance sometimes deceiving. Based on my experience, with max damage blitz needle charge I got 216 damage with crit damage colors. However, when vanaduke get poisoned by vials, I got 242 damage with normal/non crit damage colors. People said the color turned back to normal if damage is really high. Probably because it got poisoned too.