Seems like a pretty solid sale so far being that I'm sure it didn't have a ton of publicity behind it. I'll be picking up my back in about 30 minutes just waiting on that HBD to get out of savings lol.
Pretty sweet also getting the first vial discount. I'm not sure how it was calculated really but for sure a nice little perk!
It's based on the achievement, more accurately based on how many unique days you claimed during the December event. We didn't mention it back then to prevent bots to flood with accounts and there most likely won't be a similar discount now after that one to prevent future abuse, but we're glad to reward some that were hyped at the time and actively claimed rewards daily!