The Bluesky posts there basically say it all, but I am very proud of the showing my Headhunter Leviathal pulled out at the second of these events I brought it to. The first was a bit of a bust because I had to leave after only one game in which we only really played a couple of rounds, and thus didn't get the chance to really prove the list.
In a nutshell, it's designed to kill the enemy's Warlord, the model at the head of their army, for extra victory points to add to the game end tally. Most of those will come from smart primary objective play, but the points of Slay the Warlord are enough to put me over the top in the event of a draw or near draw.
It's also just a real Alpha move, a real PsyOp, and entirely thematically consistent with the lore of my army, the Alpha Legion, who thrive on sneaky, underhanded mind games they use to supplement their already prodigious capabilities as a straight up Space Marine Legion.
Pics immediately above from Echoes of Betrayal part 1 in which I played against Mechanicum.