For MD shop.

creature lock.

A creature lock prevents you from sacrificing a creature by mistake.

A moment of being absent minded and you could sacrifice that precious drachorn

When activated a drop down list with your creatures appears where you can chose the creature to be locked.

an unlock creature button appears when a locked creature is clicked inside a fenth press...

Nice, I like the idea.

Sometimes when I go saccing, I might accidently nearly click the bottom creature so "locking" it would be safer I guess.

Umm. Did you sacrifice your drachorn?

I wouldn't bother with spending a dollar on that. I'd use care instead so I could spend the dollar on something else. But if people would buy that, then all the better to make more money~

Only part I don't like is the MD shop part, it could be implemented as a freebie though ^^

EDIT: Ooh... 100 posts ^^

I agree with Glai:there are better ways to spend your money. And the issue is that some people will find it useless and if they have to buy it just to unlock other items....well....the bad words will be addressed to you