Infinite Hunger boss. Stuck on second phase, help

No idea what to do here. I'm at the second phase where it's like a wide open area with acid everywhere. How do I progress?

ps: actually the worst boss fight GGG has ever designed. I've been stuck here not knowing how to get to next phase, I'm up to 1000 corrosive stacks now...

edit: nevermind, there's a portal randomly placed in this gigantic area.

Infinite Hunger is the worst boss fight in game. The Black Star is infinitely better.

i found him in t9 area lvl 49 ... i fought him and wtf ggg , i can do easy t11 maps but this fight is the worst shit u ever made. after gettin him half down i couldnt kill him in 5 portals... i rped all my fuckin xp for what?

We were just in the same situation until we noticed that the goo flows in a certain direction, we followed it and found the portal. Edit: This method didn't seem to work as well the second time so the goo thing might not be a good method after all, sorry.