grumple %
It is virtually the best donut deal in the game, giving out a 2.00% payout increase, the same for the Stampy Parade Balloon, even though the Grumple balloon is 15 donuts less. (TO wiki)
Forum Discussion
This is easy to check. Tap your Gulp 'N Blow and find your multiplier. Then put a grumple in inventory. Wait 4 hours and tap your Gulp 'N Blow again. Your multiplier should decreased by 2. If not then the grumple balloon % bonus is not as advertised.
Edit: fixed
Edit: fixed
