Fk. That. Boss.

I don't even know what else to say.
The developers were smoking and drunkenly decided, “Let’s make a mob that will kill you instantly if you make a mistake.” And the range for this mistake is large!

p.s. If 64+ come here now with the words “Skill problem / Learn movesets” - go deeper.
This boss is just bland and difficult. Let's then do "Jump 20 times exactly every 1-1.5 seconds! One mistake - DIE!"

Just use E buff and frenzy and force brute him, not worth the time trying to do his mechanic

And because this is the go-to strat for the pit bosses you reinforce BrokenWind's point that they are all extremely horribly designed and PA can't make PvE that isn't just "make minced meat of mob packs"

Hello, I do daily pit of undying level 5 and Gotha Rensa is one of the most easy to do once you know the basics.

First of all, get as human damage as possible, because isn't capped in Pit of Undying.

Second, Know your class and cc. Even PVE only ones.

Regarding Gotha Rensa the mechanic is quite simple:
-Do as much damage as possible before 1st mechanic

-Once the 1st mechanic (and last) start NEVER use Floating or Knockback on him. Use other dps skills. (if you use some of these cc he wil get a dp buff and won't be killeable by this method)
-Don't get hit by the headbutt. 

By the end of headbutts (6 headbutts) you should have kill him but in case you didn't he will start use roaring skill

-Now you can use floating and knocback for maximise your dps

If you still didn't kill him, you have a last chance. He will teleport to the middle of the pit

-Dps him as fast as you can. You can be a bit cheesy using frontal guards at the beginning of the skill

If after all of this you still coudn't kill him, maybe you forgot to put your gear on. In that case, repeat following the recipe.

Hope this post help all the people who are struggling with Gotha Rensa!