Once again, if this is your first part of the walk-through please be ABSOLUTELY CERTAIN you are in 1.11.2 and not 1.12

 

For Phase III (The longest phase) you will see that there is a long tube made of red and block stained glass with a slime block at the bottom of it across the large gap and at the base of the gate, this is your end-point goal.  You will see The Amplification Chamber is on the same bedrock section as where you start. After standing inside of it, you can come out of it and you will be given an effect every 10 seconds. start by running and jumping over the gap, after that use jump boost to get in front of the lava, use the last second of jump boost to gain air time over the lava, and as you fall the fire resistance should assist you across, then water breathing up, the the levitation is tricky, make sure to go straight but then left a bit while still straight and then right again while still straight, finally slowness on the floating rods and jump into the pipe to the bottom and the slime block will catch you.

 

Here is the second half of Phase III, and please note: AT NO TIME IS IT QUICKER TO DROP AND TAKE DAMAGE, USE THE PORTALS. Start by going thru the gate and stand on The top of The Complex to be TP-ed into it. You are now faced with portals that save your rotation and each correspond with another in the room, start by gaining Jump Boost, and do the skulls all the way up to the portal that leads to you getting Speed Boost, this is used to clear a long jump with iron bars over your head: This jump is tricky and I suggest you don't go full speed thru the door to and back from it otherwise you will most likely fall and die. One you have the Fire Resist that is across from that jump, go to the room that has the lava in it, by going to the far left corner, on the left wall of said corner should be the door.  This leads to the end of the first save.