The trigger for him to drop the essence seems to slightly malfunction if the player's distance on the Y axis is slightly higher than his head (should be replaced by a check verifying that there's players within a 10 block radius, simply expanding the bounding box, as that expands on every axis).
Might also be a good idea to increase the death animation time, so that people can keep up with the dialogue (adding a new message every subsequent second for a 10 second duration is a bit tricky to keep up with).