If I did it right
echo '<p>Adoptables have been rearranged'.$_COOKIE->mysuid.'</p>';

then it only printed Adoptables have been rearranged.

Oh nope, the $COOKIE is a superglobal array, its not an object. You need to use {$COOKIES['mysuid']} here, if you need me to explain to you what are the differences of objects and arrays I am glad to help.

It's not echoing anything still

I see, then guess what? Do not use $_COOKIE at all, try to select uid from table prefix.users and it will work this way. In next release I will enable $_SESSION to store uid and username for almost every page, so you will be using sessions instead of cookies. For now, you have to write a code to fetch uid from database.

How do I do that? Sorry very tired here :(