The strategiy and the guidance by the dragons

Magila said :- we have 2 years to prepare igniris is preparing in the infernal volcano training his flames and his durability to be stronger than anything 

Zephyron said:- ya that maniac never stops so do you have kind of plan to beat him because we all know that only Ren could probably fight our brother 

Magila said :- yes I do have a plan big brother my plan is to isolate Ren and igniris because the battle will most likely destroye everything in their path that is why just before the battle starts me and you will transport Ren and igniris to a different dimension strong enough to handle their power but at rens current strength he would not even be able to stand against igniris 

Ren said :- why ? I think I could best him like this 

Zephyron said:- kid don't be ignorant the enimes you have fought until now we're nothing compared to our brother

Ren asked :- then how am I supposed to become stronger in such a short amount of time 

Zephyron said:- kid all you need is to control all your power into a single transformation so you could use all your abilities and strength at once 

Magila added :- then you will be able to defeat our brother 

For 2 whole years Ren trained in a single black sphere where he fought all his previous enimes at once ( the sphere was a different dimension created by Diablo and Raza 

Then after Ren finally came out of the black sphere just a day before igniris appeared Ren finally said :- finally I achieved my TRUE form the eternal devover come igniris I will fight you now