Passive until approached, then a lethal chase.
Lost Admin is exclusive to Corruption Level 2. It first spawns in a passive form that lingers indefinitely until approached, dropping a random unsettling chat line roughly once per second, "runrunrun," "THE WORLD IS BROKEN," and others.
Getting within 15 blocks switches it to an aggressive form (0.42 speed) that gives chase; catching the player within 1.5 blocks is an instant kill.