I recently started doing Enderman Slayer again. My friend had told me about people phase skipping and one shotting the boss. I decided to try and get some of the gear and see if I could one shot it too. Although I didn’t one shot it, I was beating the boss in 20-30 seconds. In this article, I will be going over the gear I used to beat the T4 Enderman Slayer in about 20 seconds.
Gear
I spent 1.6 billion coins on the gear. I bought 3/4 Crimson with Dominance/Mana Pool as well as Dominance/Mana Pool Equipment. For the helmet, I use the Wither Goggles.
Now for my weapons, I use a my Hyperion for healing. Then I bought a 500 million coin Midas Staff that is upgraded with a couple T7 enchants. 
Then I also use the End Sword to get some extra damage.
For the pet, I use Legendary Dragon Pet to kill the boss.
Other than that, I have 1280 Magical Power, and reforged to Bizarre.
For the hitting phase, I use Tank Zombies from M1.
That’s it for the gear I used. I’m still unsure how people are one shotting the boss, but I will be searching to find out how.