there is a term for your latter point:
poetic licence:
https://en.m.wikipedia.org/wiki/Artistic_license
aside: I realize i also kind of applied artistic licence in my comment here :), by not capitalizing the first words of my sentences, partly because feeling a bit lazy (on my mobile, typing is tedious and slow enough, even without switching case), and partly because I think single case (no concept of upper and lower case) is a better option.
sanskrit, for example, does not have upper and lower case, just one case, or maybe none.
go figure, er, i mean, go letter ;)
What? Where'd you learn English?
Take a look at the first two senses listed in wiktionary ( https://en.wiktionary.org/wiki/marry#Etymology_1 ):
> 1. (intransitive) To enter into the conjugal or connubial state
> 2. (intransitive) To enter into marriage with one another.
It's a transitive verb.
The problem in your sentence is that the plain form of a verb is used for states, not activities, and marrying is an activity.
"I am marrying today" is just as intransitive, but without the artificially induced grammatical error.
That's not a valid sentence, unless the person you are to wed is named "Today". Such is stuff as Abbott and Costello cashed in on.
Of course, taken in context there may be implied antecedents in spoken dialog. Spoken dialog is often incomplete and rife with implied antecedents and frequently does not follow the rules of grammer. Sentence fragments and one-word sentences can about because of that.
That wouldn't work at all; "regret" doesn't have an intransitive use. You have to be regretting something.