Ender dragon.

                           Nether 

if you want to activate  the core reactor you need 1 diamond sword, 4 blocks of gold and 20 blocks of cobblestone and a core reactor. Place the gold blocks 1 block away . put the cobble stone block between  the gold and  on top. put the core reactor on top in the middle put your cobblestone on top of that. it will start spawning  zombie pig men use your diamond sword and kill them. pick up the things that come from the core. if you want to travel to the nether than build a PC portal like this, build a rectangle  build it out of obsidian dig out the 2 top right corners then dig out left bottom middle and make them  go out farther by 1 block.then light the right bottom block.