when fighting the big dragon both heal and catapult resets his attack which means it does not damaged. this counts for both the flying attacked and his breath.
to get past fridge (level 16)you just need to put the quality on low and restart the game from scratch i.e close the browser and go back to kongregate then put it on 2x speed it worked for me.
 "Dragon Fortress"){kind=icon}
 "Snail Bob 3"){kind=icon}
 "Elemental Balance"){kind=icon}
 "UPGRADE COMPLETE!"){kind=icon}