So I discovered that if I make an angry face, my fighter fights a lot meaner and usually wins. If I am smiling, it makes my fighter weaker and I lose. But if I am making an angry expression then my tendency to rage increases, even though I am winning. If I smile, I don’t feel rage and actually congratulate my opponent for beating me badly. Has anyone found other facial expressions that work for them?
I’m honestly not sure if you’re being serious right now x’D
Not facial expressions but tea bags and taunts work well against an opponent. These are effective since it abuses those expressions that you can feel. It causes them to become reckless and create holes in their pressure in an attempt to defeat me.
However, forcing facial expressions does not assist your game play at all. It can negatively affect for mood and thus your mannerisms. But a smile or a frown can’t help you win, only can it affect your mood after the fight. Making others enraged is a much more viable strategy.
The OP may be doing things on the idea that just because they correlate that means facial expressions cause skill, which isn’t necessarily the case, but there is some science to back up the idea that we take in information in a bundle, and seemingly unrelated things such as facial expressions and how serious you take a subject matter can be tied together to where one can trigger the other & vice versa. I remember the following spring right after I first played Resident Evil (Gamecube version) I started having nightmares about zombies, because my brain had somehow tied RE to the smell of springtime (go figure 
).
Anyway, here’s an article that is somewhat related:
https://psychcentral.com/news/2010/02/01/facial-expressions-control-emotions/11082.html
This being said, I don’t doubt that your facial expressions, as well as your mood can determine how seriously you take a match, and that would likely lead to you thinking more critically about how you play.
For myself though, I just play.
Actually Kinect users can activate hidden facial buffs. It’s MS way of rewarding players that still have Kinects.
That would be pretty neat if that were true. Like Glacius would get an extra hit of armor if you stick out your tounge when he’s in instinct, or the AI increases to Kyle difficulty if you flip the screen off because you barely scrape by in a frustrating fight.