More powerful than the universe? I don't think so lol he is one of the most powerful beings but not more than the universe.
He was able to go toe to toe with him and steal the ring and become more powerful really. Surtur was able to douse out Odin and his Odin force by just holding his sword, pretty sure he could douse out and down his magic.
He hasn't tried on to many people so that list isn't to much lol. Yeah MM was able to get into spectres mind, Kulak able to influence him which is nice for and earth character to have done, Surtur had and army to take over earth and destroyed galaxies twice in his career before the making of his sword lol. Put that with his sword and eternal flame(Which can't be destroyed) he won't be beat and start the universe over again.
Oh yeah I forgot about fate, After spectre don't really have to name to much more, plus it was only two people like when Hunger took over Galactus mind what more do you have to say after that lol? So in this its who ever pretty much hits first, to destroy Surtur though you need atleast the power to destroy a galaxy.
Kulak is a powerful mage. Up there with Fate, IMO. If both are at standard levels, I see Surtur winning. If Kulak gets the ring, I see Kulak winning and putting a powerful spell on him.
I mean Fate is powerful but to actually destroy Surtur is the only way to get rid of him or BFR him. Thats why I was saying the galaxy thing because it was the only amount of power mentioned to destroy him if it hit. Yeah that sounds about right, I guess if its normal Surtur wins, If with the ring he focuses solely on the foe(rather than universe lol) than he wins.