Good game. I also personally find pressing the ''R'' instead of clicking on a restart button just as effective as having a Restart Button should you add one.
Yes this badge definitely does need a lot of build-up of exp of the characters in the game. Not even gunna bother trying for the badge of the day, but will keep going back and forth until I have achieve that badge I'll tell yous that much.
Just spent the last hour and a half earning 100 kills and was wondering if slaying 100 foes really does take all that time or the game system was not counting them properly.