To play this, you need a Water Neopet. Play this card when your opponent starts a contest. Choose 1 of your opponent's Petpets in that contest. Attach it to one of your Neopets or Heroes in that contest. At the end of the contest, discard that Petpet (it goes to its owner's discard pile).
Getting them to follow you is the easy part. Getting them to leave--well, that's another matter.