Changing the Boss Warning / No fly zone text
 

How do I change this text? It looks so ugly for some reason. I might have it altered with some addon but it's hard to find without knowing what kind of code/segment modifies this.

That's the RaidWarningFrame, and I'd guess you have an addon that's changing its scale via the :SetScale API. Due to the "bouncy" animation Blizzard added to this frame, simply changing the scale results in ugly pixellated text.