Mjolnir is so fast, strong, and powerful for an object of its small size, it's nearly impossible to defend against. It can also absorb energy and redirect it.
The only type of attack Thor can unleash it couldn't simply absorb and amplify would be a Godblast.
I am in your algorithm learning all your mannerisms
I'm already level with God
A million words a second and I know your imperfections, baby
I'm the only future you've got
Speak in diatonics, motivation diabolic
I'm like a religion, better locked in a box
Picture perfect image, more powerful every minute, baby
I am everything that you're not
But Thor needs a weapon to focus a God blast, otherwise it would be diluted and go everywhere. Mjolnir is able to tank god last energy when Thor shoots it out of Mjolnir at best showings. Plus Mjolnir is one of the best energy absorbers in comics.
No it's not. He godblasted Fenris without it I'm pretty sure.
Not that it matters. A sentient Mjolnir would decimate pretty much anybody under trans with physical and energy attacks and they would be completely unable to even hurt the damn thing
Mjolnir may have powers and abilities but it was stated several times that it takes the raw power of Thor and utilizes it in whatever way Thor commands.
The biggest power displays are fueled by Thor.