You can use someones ID as a reference code to gain a Ultra rare card and coins/money/etc, ID like Davidh2o, Ryuublade00, and Padnarok are real active accounts. Check the app store for other reference codes.

Some of those players who are giving out their ID code to be use as reference should be friend when you can as some will help you if you use cheer to send them messages.

Now onto feeding:

There are two ways to play this game in feeding.
1: Beat all the chapters using the evloved forms to upgrade your cards (usually the common/normal cards). This form is slow but it give you more points to upgrade your att, def, or energy to be able to defend/attack others or collect more cards.

2: Use a chapter 2 cards over and over and never go forward (that will make you miss out of certain cards), but this way allow you to have maxed out card (not maxed out skill however).