1. When you hit the ender dragon with bow and arrows, the HEALTH BAR DOES NOT DECREASE
2. Melee attacks against the dragon DOESN'T WORK. Only the weapon's durability goes down and they deal no damage to the dragon. Obvioiusly the HEALTH BAR DOES NOT DECREASE and THE HURT ANIMATION AND SOUND IS MISSING. Weirdly, the critical hit particle can be seen if you deal critical hit

Note 1: Tridents CAN damage the dragon

Note 2: If you destroy an ender crystal while it is healing the dragon, the dragon DOES receive damage and health bar DECREASES.