On the 'Malik created a star' thing, dunno how to feel about that. Stars and rocky planets (which is what was depicted) are composed of almost entirely different elements and even then you'd need an extremely large planet to have enough mass to turn into a star. We can either read into it and infer that Malik may have some matter creation powers oooooor use the rule of cool and accept it.
I am only nitpicking because, for the most part, WW's physics make sense. The only other example I can think of of something he was quite off on was the mass numbers on big monster cards.
To be fair, he doesn't just generate heat, he spews out actual flames, meaning his fire is actually fueled and oxidized.
While we don't actually know what his flames' oxidizer or fuel is, I think it's pretty safe to assume it's just his monster power... but if his monster power has the properties necessary to sustain flames, that can theoretically substitute for the necessary materials... mainly being hydrogen.
Let's be harsh and assume his monster power has the properties of oxygen. The fuel isn't really relevant.
Assuming he can generate enough heat (though it'd take much more than what it would with hydrogen, so more than a regular star could output) and apply enough pressure to direct the oxidizer (being mp) towards the core, nuclear fusion should be possible.
Given that we see Berny compress his wind to supposedly Planck scale, which is a FAR more impressive feat, being impossible according to physics, I don't see why Malik wouldn't be able to create enough pressure on his power to do this. And all this, is assuming his power has the properties of oxygen, which is comparatively bad for this because of its weight. Realistically, his power should be better for this than even hydrogen.
Also, what's mass numbers on big monster cards?