Went back through a few pages and didn't see any mention, but I found a lucrative glitch. Only works on first start-up though.
Go through the tutorial level until you get to the point where they give you 400 shards, and the shield woman tells you to buy a hero. Just stop at that point and put the controller down until the game returns to the main menu for idling, then start again and get back to the same point. You get another 400 shards, I ended up with 3 heros this way.
Sorry if it's already been mentioned before, can't search on mobile properly.