Mammoth is a beast of pure power. The sad thing for Mammoth is that he lacks enough speed to finish the job. Stygimoloch is faster and while not as strong he still packs a punch. One crippling bite from Stygimoloch and it’s all over. Stygimoloch gets his first win on the blog. Stygimoloch wins.
DReager1.com 
so you did it
Yeah. I’ve done every request that you requested. It helps the blog’s rep if the fans know that their requests will come fast
This one just made me laugh. Since you just used the word mammoth, this encompasses every mammoth that has ever existed.
This includes the Steppe mammoth, which weighed in at over 11 tons, aka 22,000 lbs. With Stygimoloch being a quite dubious taxon, I’m going to actually consider this under Pachycephalosaurus as that seems to be what the consensus is as of more recent scientific consensus.
And sorry, but I don’t care how fast this thing is, but a less than half a ton dino with a really hard skull is not going to be a threat to a composite mammoth that drastically outweighs it. Weight is a significant factor in real life nature, and it would be likely Pachy just gets scared off by the animal with significantly more mass than it. And if it is foolhardy enough to take a stab at trying to beat the mammoth, it’s just gonna get smacked into submission or ran into.
And no, a bite from Pachy is not crippling whatsoever. I find it unlikely it the bite can even properly get through the thick fur of the mammoth let alone cause crippling damage.
These are wild animals, not fictional characters that can properly abuse their speed in the way you’re imagining.