Originally, you were supposed to. But the creators scrapped that part of the game for some reason. If Shdwr3alm(Or however you spell his name) still came to these boards, he could post the script for that section.
and why he said he will eat mine or julius soul?
He's saying that he's not on anyone's side. He'll eat whoever's soul he can get to, without caring whose soul it is. He only hangs around Julius because Julius kills people, so Goremand can follow him, plucking souls from the bodies Julius kills.
is he the powerfullest of the game?
There's no way to say for sure. Although the creators of this game did intend to make him weaker than the main characters. However, it appears as if he needs someone to be weakened or killed before he can eat their souls. If that is true, then he is one of the weakest enemies in the game. If he actually can steal the soul of a fully healthy person, though, then he'd be the strongest enemy. Like I said, there's no way to know for sure.
Goremand was not in FFA. In fact, the remake introduced several characters who were not in the original (Isabella, Goremand, Niccolo, Li'l Cactus, the Dudbears).
Unfortunately, for the most part, all of these characters were relatively underdeveloped. /---\ So now the question for you is not 'what would Jesus do' But where will you be when the Craig Machine comes partyin' through?