Saw this slayer mob outside the door to Borealis Backyard 6 (near the TL2 terminal). Was level 200, but could be attacked by anyone, and in turn attacked everything that did damage to it, outside of PVP damage rules (halved damage/30% HP cap - it hit my 1917 HP shade for 784 points). Neither my Shade nor my Soldier were flagged when attacking this mob.
The name of the Slayer was the topic name.
Was this mob an event mob, or a horribly bugged slayer pet?