I feel like getting red cards should at least give us some money. It's really awful, if you're playing against AI, you're leading 3:1, the clock shows 10:30 and you get disqualified.
A good tip: Active the fear near the entrance, so the enemies run back and through the door. Especially useful in hard mode, since you can skip the whole wave and regenerate meanwhile.
I found a bug: bought a viking hat for my bird and now in the climbing risk game, it can't go to hide, because the avalanche will always hit it's helmet.
Right in the beginning, there's a secret button behind the right hill, which gives you a large gem after killing monsters. And the controls seem to be quite difficult at first, I can't imagine how many times have I accidentally jumped into the lake or jumped onto the treasure chest. Other than that, it's a fun game =)
I just started playing today, I'm just level 4 and I did my first arena fight. After I won I got 25k gold, all the speedy awards (i.e. winning level 53 in 15 turns) just for the arena. It's a weird bug, but it gave me a lot of extra money.
I really can't see what's the point of the stars. They don't give you any money, they don't unlock anything and instead you just have to destroy some really high hp monsters to get them and risk the chance of dying and losing the stage for something that doesn't actually give you anything.