This bug is kinda helping me around on farming mobs that I want to. I do enjoy becoming an immortal player and can kill mobs in an instant, but where's the thrill?... No more thrills, No more Hiding when a bunch of hostile mobs follows you...

I won't die or took damages from falling from high places, hugging the cactus, blown by creeper, shot by skeletons, and swimming into the lava. Insta-kill also applies to mobs, when a skeleton shoots the other mob, or when a mob hugged the cactus, etc. Pls ignore the background sound that you hear in the video, it's kinda noisy when i recorded the clips. Sorry for the resolution of the video...

Steps to Reproduce:
1. I opened my Minecraft World (cheats are not activated and achievements can still be accomplish).
2. At first, I saw a pig, I'm about to hit the pig many times until it dies to get it's loot.
3. And then suddenly, I was shocked that it dies instantly, instead dealing a a total of 8 hitpoints per punch.
4. I tried punching the cow, and it did the same.
5. After I finish farming mobs, I straight ahead to finish my house' roof.
6. I accidentally fell from the top (11 blocks), and I saw that I didn't took any damage from falling even I was wearing a full set of gold armor at all time. It must took me a 1 heart damage, but it didn't.
7. I try to drown myself and get killed by the drowned.
8. When all of my air bubbles are gone, I supposed to be drowning, screen is shaking, and taking damages from being out of oxygen underwater, but it turned up to be no damage taken and no screen is shaking.
9. After that, I wear off my armor and let the drowned kill me, but nothing happens, I'm still in full health and no damages that I have taken.
10. I punch the drowned and it dies instantly.
11. I return to the main menu and saved the game.
12. I reboot the app, and played the same world again.
13. The bug happened again. So I exit Minecraft and I reboot th e App Including my Device.
14. When I played Minecraft Again, the bug Happens again.
15. I Tried it on Creative mode, I punch a various mob and they die instantly.

I added two new clips... I tried defeating the Wither in creative mode with One Punch, and the wither dies without going to it's agitated form.
I tried defeating the Wither again in survival mode, the Wither dies with the single arrow, My player is safe from explosion, but not on wither's effect... I died...