Fair enough. But let me put on my lawyer hat (i.e., go to Wikipedia, try to find a pertinent precedent, find the actual opinion, and quote like hell) and see what I can do. ...
I reference Campbell, aka Skyywalker, et al. v. Acuff-Rose Music, Inc. from the United State Reports Volume 510: Cases Adjudged in The Supreme Court at October Term,1993 (PDF page 773).
Concerning the fair use defense of 2 Live Crew to parody Roy Orbison's song "Oh, Pretty Woman", to quote Justice Souter's opinion for a unanimous Court decision (pp. 782-783):
The first factor in a fair use enquiry is ... to see ... whether the new work merely "supersede[s] the objects" of the original ..., or instead adds something new, with a further purpose or different character, altering the first with new expression, meaning, or message; it asks, in other words, whether and to what extent the new work is "transformative."
I would argue, thought I'm sure not without debated, that POWER/RANGERS fulfills this transformative requirement of fair use.
Concerning the issue of parody, Justice Souter goes on to say (p.784):
For the purposes of copyright law, the nub of the definitions, and the heart of any parodist’s claim to quote from existing material, is the use of some elements of a prior author’s composition to create a new one that, at least in part, comments on that author’s works.
POWER/RANGERS offers the perspective, or critique, of teenagers being recruited to fight an intergalactic war with more actual war-like elements that stand in stark contrast to the light-hearted portrayal of the sampled work. It mimics the characters and world but does make a point: war isn't as fun as was shown.
Concerning the issue of excessive use of elements from the original work, the Justice says (p.792):
Parody presents a difficult case. Parody’s humor, or in any event its comment, necessarily springs from recognizable allusion to its object through distorted imitation. Its art lies in the tension between a known original and its parodic twin. When parody takes aim at a particular original work, the parody must be able to “conjure up” at least enough of that original to make the object of its critical wit recognizable.
I would argue that the author of the work in question took as many elements as needed to make the parody recognizable to the audience such that the parody would function. In taking those elements however, the author did transform a number of aspects to suite the intended parodic purpose of the piece (e.g., newly added machine guns, Bulk and Skull turning homicidal, the protagonists losing and dying).
Lastly, concerning the economic incentive, the Justice states (p.794):
[The fourth fair use factor] requires courts to consider not only the extent of market harm caused by the particular actions of the alleged infringer, but also "whether unrestricted and widespread conduct of the sort engaged in by the defendant . . . would result in a substantially adverse impact on the potential market" for the original.
Since the work is blatantly made without the desire of monetary feedback, is not intended to supersede or replace any of the extant or future productions of the original work or author, and has done nothing but bring attention to the original work through this parody, the fourth factor of fair use is satisfied.
But again, I'm no lawyer. I just play one on Slashdot.