Thanks, 3run!
I was finally able to solve it. For some reason, global variables didn't work. So I declared the variables inside my player's function and extracted the numbers like so:
Code:
function PlayerMovementFunction(MONSTER* Mon)
{
	STRING* AbyssNameString = str_create("");
    STRING* AbyssNumberString = str_create("");
    STRING* TempString =  str_create("#10");
while(1)
	{
		vec_set(vMin,my.x);
        vec_set(vMax,my.x);
        vec_add(vMin,my.min_x);
        vec_add(vMax,my.max_x);
        
        //CHECK IF PLAYER HAS FALLEN INTO AN ABYSS REGION, THEN RESPAWN HIM AT CORRESPONDING RESPAWN POINT
        if(region_find(AbyssNameString, my.x))//check if ent is in region & store name of region
        {
        	str_cpy(TempString, AbyssNameString);
        	TempString = str_cut(NULL, AbyssNameString, 1, 5); //store first 5 letters in TempString
            if(str_cmpi(TempString, "Abyss")) //if the region is an abyss
            {
        	    str_cpy(AbyssNumberString, AbyssNameString);
        	    str_clip(AbyssNumberString, 5); //Delete first 5 characters then store resulting number
                if(region_check(AbyssNameString,vMin,vMax))
                {
             	   vec_set(my.x, Player1RespawnPosition[str_to_num(AbyssNumberString)]); 
                }        	
            }        
        }

I decided to name any Abyss region that isn't a double digit as Abyss01, Abyss02, etc. It still works that way, and I doubt I'LL ever have up to 99 Abysses in a level, so I can safely hard code lines like "str_clip(AbyssNumberString, 5);" knowing that my Abyss region names are always 5 letters followed by 2 digits.