Remember in The Lord Of The Rings: The Two Towers when Gandalf falls down the big chasm with the Balrog, smacking the sawdust out of it while plummeting towards the waters of the underworld? Well, give Gandalf a gun, play that sequence in reverse, and swap the Balrog for a flock of Space Invaders, and you are playing something like the demo for Dwarf Legacy – a “bullet-hell precision platformer” from Wulo Games about a dwarf clambering up the inside of a mountain.
Oh wait, Gandalf needs to be listening to crunchy dancefloor music to complete the analogy. Also, he needs to stop periodically to buy better guns from a blacksmith. I’m pretty sure this is still within Peter Jackson’s budget.