Hogger.
Its going to be Hogger and it all makes sense.
In Brackenhide Hollow, we can see the extent of decay magic and its self-destructive but extremely potent power. The final boss, Decatriach Wratheye, is able to escape last minute.
Now, we dont yet know where she went, but we can make educated guesses! Before she teleports away, she makes threats about how all will wither away… but clearly she alone isnt powerful enough to back these up but do you know which gnoll IS powerful enough to do such a thing? Thats right, the Scourge of Elwynn himself, Hogger!
But you may be asking, “Wait… we killed Hogger in the stockades right?” Well, yes, we somehow managed to beat Hogger in the stockades (clearly he was using less than 1% of his true power) but it doesnt matter. Wratheye clearly teleported right to where Hogger was buried and is planning on resurrecting him to fight us once more.
“Erm… ackshually decay magic hasnt been shown to be able to ressurect people-” SILENCE!!!
Galakrond, you all know him, shows traits that are very similar to that of decay magic. Galakrond was able to infuse proto drakes with powerful but also self-destructive magic (sounding familiar?) which also was able to resurrect SUPER POWERFUL UNDEAD ZOMBIE PROTO DRAGONS! So whos to say Wratheye cant do the same with Hogger?
Hogger will most likely come back in the final patch along with Wratheye and insta-kill the primal incarnates with his mighty level 9 green axe and absorb their power becoming Hoggerkrond and an unstoppable monster.
Honestly pretty predictable, but this final boss is gonna be so awesome nevertheless.