Upgraded End Fight tweaks various things about the classic end fight in Minecraft. Using Skript, we have created 3 total phases.

Phase 1:
Phase 1 starts with the normal ender dragon as the boss, that's it, for now.

Phase 2:
Phase 2 starts when the players defeat the ender dragon, and are greeted with text that states they have defeated the end, or have they...? Players are trapped inside of the End dimension, to fight off a wither, as the second phase of the end fight.

Phase 3:
Phase 3 starts with mobs such as vindicators, ghasts, and wither skeletons, that spawn around the end island, once you have defeated the final phase, you may now exit the end, keep in mind, the skript disables you from returning to the overworld via the end portal after the first phase is done. You also cannot go to the end islands.

Commands (Most are for server operators):
/setdragonphase <number>: sets the current phase of the end fight, from 1, 2, and 3
/resetphase3: resets the mob kill count for the phase 3
/whatisdragondeadat: sends what phase you are on
/whatisphase3at: sends how many mobs you have killed during phase 3.
/revive <player> revives a player if they've died in hardcore
/endfightsettings lets you change the hardcore setting (also used with /efs)

Hardcore system:
After you have done all 3 phases, you will be allowed to leave the end, HOWEVER, after this point, if you die, you will be put into spectator, making it hardcore. There is a /revive <player> command, to revive someone if they have died. If you do not have the resources in your inventory, the skript tells you what you need.