A Hard stamp was a stamp type you could get on the lost game, FLUFFY CLUB. There are 2 of them. (Sea fluffy prize, Fluffy birthday.)
Sea fluffy prize:
This stamp could be earned by catching the extremely rare sea fluffy. though it is lower to the harder levels it is a challenge to get as a 1% chance of catching a fluffy is possible.
This stamp could be earned by joining your fluffy's birthday. it could also be earned by going to 10 more fluffy birthdays.