PSA - My guide on maximzing your snowdown odds and not getting screwed on chests
Here's how you should approach all snowdown related things:
Legacy skins:
THIS IS THE TIME TO BUY THEM IF YOU WANT ANY OF THEM. They will not be on sale until next Snowdown. If you want any of them, take the money hit and buy them now, because it's your only guaranteed chance to get them this year. If you are ever going to splurge, now is the time. I waited from August to get some of these and it was a long and frustrating wait.
**Themed Snowdown Chests: ** ABORT, STAY AWAY FROM THIS. This is risky as hell.
Let's say you want 1 skin from the day's special snowdown chest theme. If I wanted Heartseeker Ashe, I'd have a 1/11 chance of getting it, which is 9%. Now, you can get duplicates. I don't know the odds of them, but you might as well cut your odds in half knowing that. You can only buy 6 chests a day for a total of 1,770 RP. Finally, and this is also a big one, you are getting skin shards not actual skins. You will need Orange Essence to enchant any skin you want and that's another form of currency that is also quite expensive.
Please don't buy these. Your odds are less than 9% of getting 1 skin you want. Just wait for the skin to go on sale for 487RP/675RP or whatever and buy it then. Save yourself the money, time and frustration. You likely aren't getting the skin you want unless you are super lucky.
Mystery Champs
To maximize your chances, you need to buy all 450, 1350 and 3150 IP Champs before buying any mystery champs. This will take all of these out of the equation and ensure you only get 4800IP and 6300IP champs. Why is this important? 4800IP champs cost 440RP to 6300IP champs cost 487RP. Since IP is terribly expensive and should only be used on Runes, it is much better to lose 3RP or 50RP than to lose 198RP on 1350 IP champs and 95RP on 3150 IP Champs. Getting any champ through mystery champs worth 3150 or less is a waste of your money.
If you want a specific champ, don't do this. If you are looking to complete your champ collection, buy buy buy. Not only will it save you money now, but once you have all of the champs, you will save IP and will be able to get release day champs for IP with Mystery Champion Shards.
Mystery Skins
Again, DO NOT DO THIS IF YOU WANT A SPECIFIC SKIN. The odds are not 1/900+ on which skin will appear, and that's without counting duplicates. You will not beat the odds here.
When should you do this? If you want skins and don't care what you get. The good news is that you actually get the skin here, rather than a shard.
Winter Chests
Stay the hell away. These are almost as bad odds wise as the Themed Snowdown Chests. You are getting shards, not skins and not champs. All of these cost essence to enchant and you need 3+ shards to activate one. The odds are also not fair since you can get duplicates. Horrible deal and a total waste of money.
Legacy Skin Chests
This one is interesting. Legacy skins are only available through: 1) Hextech, 2) Bundles, 3) Events like Snowdown/The Harrowing. #3 is only twice a year and #1 are risky as hell.
When should you not buy this? If you want a specific skin because your odds suck.
When should you buy this? If you have the legacy skins you want already because you listened to me and took the offer while you could, and just want rare skin shards.
Remember though, you are getting shards here. It can take up to 3-5 shards to activate 1 shard. If you don't have enough, you have to buy more shards or have to get S-'s and have enough champs to get multiple S-'s with, and hope you unlock more shards to disenchant with.
We don't quite know the odds here and you will likely get duplicates, but if this entails all legacy skins, this may be your only chance until next Snowdown/Harrowing/Lunar Revel to get some of these skins.
Bundles
These are more for people who have every champ. You don't want these to get champs, because the champs are all cheaper on sale. Just do the math you'll see it won't add up. These are definitely not worth it if you want one specific skin or champ. I would just buy them outright, get the thing you want and be happy.
Feel free to ask me any questions and please don't be a dope and waste your money.