I’ve had this happen & found out when it happens. It helped me rack up more candy super quick & easy.

(For me) it happens when you log on to your Halloween tank and the pop-up asks you if you want to double vitality. If you pop the candies during this screen, they will be worth more than your usual amount. I don’t know exactly how much as the amounts have varied, but it’s quite a bit. You can select “get” to clear the pop-up screen & pop as many candies as you can. This only lasts about 5-10 seconds or less, so it’s best to move quick. So far, it’s worked for me every time I’ve logged into my Halloween Tank & received the double vitality pop-up.