You are the single-vowel word:
Add a consonant up front: I become deadly
Add an 'S' to the front to get SWORD, a deadly weapon.
Add a consonant inside: I become a very big place
Add an 'L' inside to get WORLD - a whole planet!
Replace the end consonant: I become a living thing
Change 'D' to 'M' to get WORM - a living thing.
Replace the front consonant: I become powerful
Change 'W' to 'L' to get LORD - a powerful master.
Turn me around: I become-kind of-wet.
Reverse WORD to get DROW - a Scottish word for a gust of wind and rain.
You really are everywhere, aren't you - especially in this puzzle...
...not just in the form of miscellaneous words on this page, but you've also been explicitly mentioned three times in the text and again in the question tag!