Lin Fan laughed not because Abaddon had done anything comical, but because as his memories returned, more and more details about Drach'nyen surfaced in his mind. The stark contrast between those details and Abaddon himself was what truly made Lin Fan laugh out loud.
Drach'nyen was a daemon specialized in posing an extreme threat to The Emperor and humanity. During the Webway War, Drach'nyen's record had been truly terrifying. He destroyed a combined force of Adeptus Custodes, Sisters of Silence, and Titans. He moved through human bodies, possessed the princeps of a Reaver Titan and destroyed a Warlord Titan, then possessed a Magos Dominus and destroyed an Adeptus Custodes Dreadnought. This daemon had even grievously wounded The Emperor himself. Unable to destroy this daemon born from humanity's primal malice and bound to him by countless threads, The Emperor could only seal away its power and banish it beyond the Webway.
Thinking about it that way, Abaddon really did not have as much gravitas as Drach'nyen. Thinking even further, perhaps the current Abaddon was holding back Drach'nyen's power. Just as he would later waste the irreplaceable Blackstone Fortress by using it as a meteor to smash into Cadia.
Abaddon: Ah! Drach'nyen! The daemon sword capable of harming The Emperor's true body! With it, I will utterly crush the Imperium! Destroy that liar on the Golden Throne!
Drach'nyen: Can't be bothered with this idiot. I'll just turn into a sword so he can use me.
Moreover, Abaddon's experience obtaining the daemon sword was rather interesting. He had wandered through a labyrinth filled with impossible angles, where he encountered a towering figure shrouded in golden light. That golden figure led him to the center of the labyrinth, where the sealed Drach'nyen floated.
If that golden figure had been The Emperor... then there were