I think there's plenty of reason to assume that the energies in Mjolnir are part of the godblast.
All of Dr.Strange's spells utilize external energies, yes.
There's no point in analyzing what is considered Dr.Strange's energies or not, though, as using a spell is considered different to throwing a punch or shooting a beam of energy
The fuel for the Godblast isn't power. It's lifeforce. Longlevity. Thor sacrifices dozens or hundreds or whatever years of his life to deliver a powerful blast and finish more powerful opponents. It's the Genkidama of the Marvel universe.
In another example we saw Doctor Strange using powerful magic and monks having to sacrifice their own lifeforce to pay for that magic. They were in antagonizing pain. But when Sentry gave away his lifeforce for it, he wasn't bothered by it at all – since he is in fact absolutely, positively immortal. Where someone like Thor just lives long.
So Sentry is still more powerful than Thor, but I don't think that he is beyond the damage the Godblast can inflict. And the Godblast is fueled by Thors lifeforce and not his overall power. We saw that Thors overall power couldn't really stop the Sentry, when he tried to brawl with him. And we saw that an enraged and later on even amped Thor couldn't finish the Sentry with his lightning.
"I must call forth the godly lifeforce which flows within all Asgardians - and grants us our very immortality -- and I must channel it through my enchanted hammer in one great, destructive blast."
Thor sacrifices years of his life to fuel the Godblast. Why is that so hard for you to understand? That's like the most basic Marvel comics Thor knowledge.
Pretty sure Captain Marvel has magic resistance/immunity.
And he did survive being turned inside out.
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Well, I suppose the discussion on the exact properties of the godblast is a bit peripheral.
All we know is that it's Thor's best attack, it requires his life force and it has to go through Mjolnir.
Thanos would take the blast and smirk. He took a blast from the Galactus Thanosai and lived. That guy was stated to be more powerful than Galactus himself.
It depends on how you want to judge the Juggernaut's durability while handled by different writers. One writer had him nearly burned to death by the flames of a chandelier, while another portrayed his forcefield to be tough enough to withstand Thor's godblast.
Funny how it depends on the writer now. BTW in the previous comic the force field appeared in Juggernaut at half power was hurt by a gas tank explosion/a building falling down on him and shit like that.
But no, those showings don't exist. Averages are for other characters, not for Godblast and Juggernaut's force field.