It's bad. Don't do it. Icky grammar. We're not telling the future here.
This also extends to combat RP (sorry to those who believe it's useful there, but it's really not).
Saying "She would punch him in the face" seems to A) imply that she would have done this had something not stopped her (see Kismet's "mauled by a bear" joke above for reference), or B) if we're going by the assumption that all the "woulds" of those who write in future tense are/will be completed actions, it can be interpreted as auto-hitting just as much as "She punched him in the face" or "She punches him in the face" could.
Instead, "She swung a closed fist toward his face in a punch." (Or "She swings," for those who prefer to use pretense tense.) There is not autohit or godmodding. There is no assumption the punch will hit. The swing, however, is now cemented as something that certainly did happen (or is happening, for present tense).
Editing to add:
Some people use it for variable conditions such as, "She swung a closed fist toward his face in a punch... if the punch hit its mark, she would then kick at his shin." This isn't the only way to write something like this, however, and is probably not even the best way. One option is to simply wait for the other role-player to respond to see if the punch hits, even if it makes the post shorter. Short posts aren't inherently bad. Combat posts with a character making several actions/attacks become messy and confusing at best, and annoying and god-moddy at worst.
The other alternative is posting something along the lines of, "She swung a closed fist toward his face in a punch... if the punch hit its mark, she then kicked at his shin." The variable is still there, without the "would." No more awkward tense switching mid-post. The sentence flows better, is shorter, and has less unnecessary clutter. The meaning is still the same and just as easy to understand.
This also extends to combat RP (sorry to those who believe it's useful there, but it's really not).
Saying "She would punch him in the face" seems to A) imply that she would have done this had something not stopped her (see Kismet's "mauled by a bear" joke above for reference), or B) if we're going by the assumption that all the "woulds" of those who write in future tense are/will be completed actions, it can be interpreted as auto-hitting just as much as "She punched him in the face" or "She punches him in the face" could.
Instead, "She swung a closed fist toward his face in a punch." (Or "She swings," for those who prefer to use pretense tense.) There is not autohit or godmodding. There is no assumption the punch will hit. The swing, however, is now cemented as something that certainly did happen (or is happening, for present tense).
Editing to add:
Some people use it for variable conditions such as, "She swung a closed fist toward his face in a punch... if the punch hit its mark, she would then kick at his shin." This isn't the only way to write something like this, however, and is probably not even the best way. One option is to simply wait for the other role-player to respond to see if the punch hits, even if it makes the post shorter. Short posts aren't inherently bad. Combat posts with a character making several actions/attacks become messy and confusing at best, and annoying and god-moddy at worst.
The other alternative is posting something along the lines of, "She swung a closed fist toward his face in a punch... if the punch hit its mark, she then kicked at his shin." The variable is still there, without the "would." No more awkward tense switching mid-post. The sentence flows better, is shorter, and has less unnecessary clutter. The meaning is still the same and just as easy to understand.