User blog comment:BlackWizardZeref/Fairy Tail: Chapter 380 Hell's Core/@comment-7418318-20140411142701/@comment-59.184.166.54-20140411143814

He could be something like Bluenote...On the other hand, he might also be something like Brain/Zero, with E.N.D. being the darker, more powerful half...only difference between the two being that while Brain required the others to be defeated to release the spells on Zero; E.N.D. may just need time/souls/power/trolling/etc. to awaken and tek over Marde Guille's body...

Only time will tell...