This is not plagiarism
Plagiarism is the use of another person's ideas or work (especially direct quotes or close paraphrases) without attribution. While it is not strictly a legal concept, in academia and certain other contexts, it is considered serious misconduct and a form of academic dishonesty that can be grounds for revoking a degree or award, for refusing to grant an academic title, or good cause for terminating even a tenured professor from his or her employment.
Plagiarism used to obtain an academic credential, which, in turn, causes someone to secure a job is considered a form of employment application fraud by many employers that could result in the termination of the person's employment, particularly if the credential is a master's degree with a thesis requirement or a PhD and the plagiarism is in the thesis or dissertation which was required to obtain that degree.
If an academic credential is relied upon as a credential when seeking a political office, plagiarism is often considered grounds to vote against the candidate or to ask for their resignation. In a parliamentary system, cabinet officers who were found to have engaged in plagiarism for a credential relevant to their ministry assignment will often resign at the request (actually a polite demand) of the prime minister (or in the case of the prime minister of other influential party members or the President or constitutional monarch).
Referring to someone else's ideas or work is actually welcome in academic writing, and attribution may be by footnote or endnote, by a short form reference in a text accompanied by a bibliography, by a hyperlink, or in the body text in the vicinity of the reference. As applicable to you, and as is common particularly in editorial cartoons and video or audio reporting/comedy, there are some references which are so widely known that making them is an implied attribution even if none of the formal methods of attributing a reference are used.
For example, if someone says "A Rose By Any Other Name Is Just As Sweet", there is an implied attribution to the Shakespeare sonnet, even if no formal attribution is given and this is not considered plagiarism. Similarly, in physics, if someone says regarding an experimental result in a physics paper, "Who ordered that?" or "God doesn't play dice with the universe." or one talks in economics about "lassiez faire", those quotations and ideas are so famous that a lack of formal attribution does not constitute plagiarism.
In a fictional work, such an unattributed but clear reference is considered an "homage" rather than plagiarism. In a related notion, in fiction, the "scène à faire" doctrine of copyright law provides that certain tropes derived from other writers works are not considered copyright violations (and are also not considered plagiarism) if they are genre conventions using by many different works in the genre that help define it.
Visual or express references to Spiderman, Deadpool and Star Wars or Dragon Ball Z characters, presented to an audience in which many members of the audience are familiar with these famous characters are not plagiarism because there is an implied attribution. Everybody who recognizes these characters at all knows obviously that you are not really claiming to have created them and that their true creator is widely known. Even though you tag it as an "original work", it is clear that you are not claiming to have invented these characters and this is clear to anyone in the intended audience.
If you wanted to be squeaky clean on the plagiarism front, you could including a fine print disclaimer with each comic having the characters stating that "Spiderman is a character created by Stan Lee and . . . for Marvel Comics and I make no claim to being an original creator of this character.", or something similar as the case may be.
Copyright issues
Your comics are almost by definition "derivative works" because they are based on the copyrighted work of others, so they are infringing the copyright of the persons owning copyrights to those works, presumably without a license from the owner of the copyrights to do so. But, parody is one of the best established, clearest and broadest categories of fair use, which is a defense to a claim of copyright infringement, to the extent that it is almost a separate defense.
So long as what you are writing is truly parody, and not merely humorous "fan fiction" (i.e. an infringing derivative work in which you use the characters and worlds originally developed in the source author's works as an expansion of the original author's works in that world, rather than as a parody of the original work), you have a strong fair use defense and have not violated copyright law.
A "humoristic comic" use of protected characters is not necessarily satire or parody, although it could be, as satire and parody are usually (although not always) funny, at least in a grim humor kind of way. If Spiderman and Deadpool are being used to make fun of government policies rather than, for example, fighting crime, there is a good chance that it is satire and protected. If Star Wars characters are being used to mock the original franchise (e.g. in a piece pointing out all of the safety regulation violations in the Death Star such as a lack of hand rails), this would safely be parody.
But, if one of these characters is merely used to present new examples of the kind of humor present in the original works, the satire and parody defenses of fair use and whatever it is called in the trademark context, would not apply.
It wouldn't hurt to put a disclaimer stating, "This comic is intended as satire and parody, and is produced without a license from the copyright owners of the original works implicitly referenced in this comic.", so that your intent is clear. This isn't an absolute defense. Saying it is a parody or satire does not make it so. But, this could clarify your intent in a close case where your parody or satire intent is more obscure than you had hoped that it would be.
Trademark issues
The case of trademark law is trickier. Most famous fictional characters of major multi-media fiction producing empires like Marvel Comics, the Star Wars franchise, and major anime series, are protected not just by copyright but also by trademarks covering all developed work countries in many major product markets including but also apart from just comic books, and furthermore these trademarks have extra protections associated with "famous" trademarks, and are "incontestable" due to their age.
Despite widespread inaccurate beliefs to the contrary, a trademark is not an exclusive right to use a word or image or other distinctive thing with "secondary meaning" that associates it with the trademark owner. Instead, trademark rights protect the owner only from the use of a trademark to sell goods or services in a product market covered by the trademark in a geographic area to which the trademark extends.
The classic trademark violation is trying to, for example, sell knockoff shoes as "Vans" when they are not made under license from or in association with the company that owns that brand name, in a way that misleads the customer (it is legal to have a labels that says "compare to Vans" thus making clear that it is not actually a product belonging to that brand).
There is also a less well established and less clear, but meaningful, parody exception to trademark infringement.
Using trademarked famous characters in a non-parody way in connection with the marketing and content of a comic would be a trademark infringement as well as a potential derivative works violation of a copyright.
You could also argue that you aren't using the trademark to sell a product (so called "nominative use"), but are instead being used to compare your product or to reflect their presence in daily life. However, if these characters are integral to your comic and its appeal, as opposed to a mere nominative use, this won't help you either.
For example, if you have a completely original character say in passing "Spiderman never pooped in his suit.", that would probably be an homage or a nominative use which would be acceptable. But, if you had Spiderman and Deadpool engage in some physical humor of the kind they do in the comics and movies, this would probably be an infringement.
Practical considerations
The corporations that own the rights to the characters you have mentioned are billion dollar companies with an intense interest in protecting their intellectual property, so, in a close case, even if you ultimately win, you could end up in a very expensive legal battle against an opponent with deep pockets and a strategic and economic interest in pushing the extent of their intellectual property protections to their maximum extent. So, even if you are probably in the right, you may want to tread carefully in areas that are probably gray areas because you can afford to fight that kind of litigation without outside help which may not be available if your case doesn't look obviously sympathetic on the merits.
