Skypig, shut up. you find your refund code, not keep it. Greatninja, hp is for when the enemy uses spells or when they have monsters that can attack your monsters. Defense and HP comes also in use when you have permamonster or lure
Also note that gambling in the shop has NOTHING to do with either your luck or the characters luck. The item you will get is PRE-DETERMINED by the random generator, and you can choose to buy it or not. When you buy it, it doesn't give you a random item of that type, the item is ALREADY SET, but it just won't tell you the STATS of the item, or the rarity. Keep this in mind when you gamble
If you don't know, here is a tip: Don't use the color item filter. Note that if you hover over an item, you will see: White stats, green stats, and blue stats. White stats are NOT INFLUENCED by rarity, so you can get a white weapon that deals 100-140 damage and the same monster can also drop a legendary weapon that only deals 10-14 damage. Necklaces, however, only have green stats, so white rarity necklaces=useless. Green stats are stats gained by the rarity, so you may see items that such have +1 strength in white and another +1 strength in green. Blue, is very obviously the stats gained by blacksmithing your items. Take this seriously.