This question or variations on it, get asked a lot. I won't go into great detail now, but perhaps someone else will. Suffice it to say that "fair use" is an affirmative defense to infringement and must be proved by the party asserting it. There are multiple factors that go into a fair use analyses. Even a successful fair use defense can likely mean you've spent at least tens of thousands of dollars in defending yourself. Your idea, simply put, is very risky. Try doing something completely original and you won't have to be worried about expensive copyright or trademark infringement claims.
I am not your attorney and any posts/messages or responses to posts/messages can not establish an attorney-client relationship. www.PatchogueAttorney.com You should not rely upon free legal advice and I disclaim any liability for the results if you do.
Hasbro aggressively enforces its IP. If hasbro finds out about this expect a C&D letter at a minimum. If you are making these as promotional pictures to display your talent you will have the competing interest of wanting people to admire your work while fearing litigation.
Fair use is an affirmative defense that comes at the end of litigation. It does not prevent a suit from being filed against you. That suit could cost you several $100,000.
Or you can try to get a license to make your work...
Better you display your talent in a way that you can actively promote without the fear of litigation. Get a license or choose different subject matter.
I think you would have a reasonable possibility of convincing a Court that your use of the characters constitutes a parody, which is protected by the fair use doctrine. The problem, however, is that fair use is only a defense to a law suit. There is nothing to prevent you from being sued even if you have a solid fair use defense, and law suits are expensive.
There is substantial recent case law supporting the right of artists to create "transformative" original works based on famous celebrities or characters, It sounds like you would get the benefit of this case law if you had to fight this in court. I sympathize with artists who wish to engage in projects like this involving truly transformative, creative, uses of existing characters. Trademark law is designed to prevent consumer confusion as to the source of goods and services, and I seriously doubt if your use of the trademarks as described in your question will cause consumer confusion.
Nonetheless, this remains a rather risky business---not because the law is against you. It is simply a fact of life that a big company such as Hasbro has the resources to make your life miserable in a law suit, and probably don't have the ability to fight back. Note that despite these risks, many artists engage in projects like this every day without getting in trouble. Ultimately, only you can decide whether to take the risk.
Just like with any other business, you need to consider the value of the project to you versus the risk of litigation. If Hasbro is litigious, then you might reconsider relying on fair use because fair use is an affirmative defense. Because it's an affirmative defense, there's the possibility of having to go through litigation and spend a lot of money just to show that your defense is good. It's a business decision.