And holy crap it is tough! (Story ahead)

Background: The map of the server I tried it on was from 1.8, so the dragon was already dead. The difficulty was on hard. My base was ~45 minutes from the nearest stronghold, and I didn't set my spawn there so I wouldn't have to run 45 minutes back to my base after defeating it. I even brought a fried with me to help, so I imagined it would go smoothly.

The actual fight: After we got into the end, I placed the crystals to resummon the dragon. While the animation was going, my buddy looked at an enderman and got torn apart, even though he was wearing enchanted diamond armour. While he was running back to the stronghold, I was fighting the dragon, and it was going pretty well (<50% health). Then, disaster happened when my chestplate broke and endermen ripped me apart, while teleporting away before I could hit them back.

With both of us dead, we met up again after a long walk. I brought a new chestplate and some food with me, and jumped back into the portal after eating a Notch apple my friend gave me.

The apple ended up saving me, as the dragon knocked me about 30 blocks into the air, just before getting my feather falling boots back. With both of us geared up again, we brought the dragon down to 25%, when my companion unsuccessfully tried to bath in dragon's breath and died for the second time. Although endermen kept giving me a hard time, I was finally able to kill the dragon in 1.9!

TL;DR Endermen OP

PS: sorry for the bad sentence structure.