Pseudonymous is a great word and just the longer version of pseudonym. The Internet has given rise to pseudonyms in the form of avatars and usernames as a common practice. Most of us know what a pseudonym is, a false name often used by writers or novelists to mask their real name.
Mark Twain was really Samuel Clemens and “mark twain” is a phrase used by a steamboat crew to indicate the depth of a river. The term mark twain indicates a depth of two, two fathoms or about twelve feet. Having worked on a riverboat Clemens would have used the term often.
In the world of acting, we call pseudonyms “stage names.” Winona Ryder is actually Winona Laura Horowitz. Tom Cruise’s real name is Thomas Cruise Mapother, IV. Michael Keaton was born Michael John Douglas. Sometimes pseudonyms are used to mask an identity, and sometimes to create a more appealing name for the stage. And then there are pronunciation issues for some. Natalie Wood was born Natasha Nikolaevna Zakharenko, just too much of a mouthful for movie goers.
Pseudonymous is the adjective form of pseudonym. And then there is pseudonymously an adverb, and pseudonymousness or pseudonymity both nouns.
“The documents obtained by Congress confirmed the claims by pseudonymous whistle blower ‘Deep State.’”
“The claims made by the pseudonymous ‘Arrow’ have proven to be true.”
“Unknown to most, public nature of blockchains makes them easily pierced because they are based on pseudonymity.”
The use of “Impactful” is a good debate discussion and it would seem that the first use of the word dates back to only the 1960’s. Some dictionaries classify it as a real word and others see it as just slang when better words are available. We seem to know when the word is used the speaker or writer is trying to convey that something has great influence. But for many editors it is a meaningless slang term used by the poorly educated.
Many who argue against impactful point out that the English language has many more words that do a better job of conveying meaning. In this list are exciting, passionate, meaningful, eloquent, expressive, touching, and many more. If you decide to use impactful people will understand your meaning, even if it is a less desirable word.