my opponent played the location card :
Ruins of an Ancient Civilization
Whenever a character deals combat damage to your fortress, that character is removed from the game. It returns to play at the end of the next turn.
I had several enraged creatures out, for example:
Pay 3: Enrage 6
(Pay 3 to enrage this character, giving it +6/+6. This ability can only be used once.)
So I enraged him, attacked with the now 13/14 enraged hulker. he gets removed from the game, when i get him back he is still a 13/14 and it lets me enrage him a gain, making him a 19/20 enraged hulker.
I made a deck with a few self removal cards and tested it against puffy and it works consistently. removing something from the game seems to clear the enrage history on the card but keep the stats.