@TheMinecraft13 You can get more by equipping items that give you it ( hover on an item for info ). Or, just pay Pixels to get some ( via Stats screen ).
Seriously, I remember back in 2009 and 2010 where comments were all about epic suggestions. When the game got a forum, all the suggestions went there, leaving this the place where... actually I don't know what is being post in the comment section. It's empty after the addition to the forum. Just saying.
@ghostxtr You get extra EXP from the monster which you have the ally mastered for, and it also has a higher chance to appear as a Rare monster. It also has a higher chance to appear as an Epic monster on Worst Moon.