I have the same problem, if you go into one of the portals the distroyer armour guy dissapears and all the other portal doors close when I go to them. So I restart and than attack the never-ending supply of trolls until my hands hurt as I watch the destroyer armours damage bar reset when it gets full. Maybe it's a game disfunction. Sometimes when I go into the portal where u chase that sword, the game doesn't transport me back to where the destroyer armour lies so than I havto start all over again. I've beaten the game once but this part is just pissing me off!

SOMEONE ANSWER ASAP! (I read the other answer but it didn't work)

well at the start you'll see loki's body going into one of the portals and den his spirit into the destroyer armour, dun waste time hitting him, lure him to the portal which his body went into, den enter de portal, you'll find urself in a new room with de destroyer armour and loki's body, den you start filling up his gauge he'll kill loki's body XD man it took me forever to discover dat..-.-!

Im stuk on da sam prt but a few dayz ago i lured da destroyer armor into da portal n found
loki stuk in ice so i destroyed him and beat da destroyer armor. aftr dat, dr.doom thought
he killed me but som creepy azz hole saved me n sent me 2 da moon wher im suposed 2 get
som rok or crystl to save odin from dr.doom. but dis peice of **** game fukin froz on me
B4 i got 2 sav da game.now im tryin 2 beat ultron n dat othr fagit n then beat loki n da
destoyer armor agen but wen i try 2 chase da sword in dat portal it wont teleport me bak
so i keep loading bak da gam. i kno dis **** waz long, sorry

AFTER YOU BEAT ULTRON AND BARON GO BACK TO THE SAVE POINT AFTER YOU BREAK THE BARRIER WITH
ODIN'S SPEAR THEN SAVE IT THERE TO SAVE VOU THE HEARTACHE.