The RoCitizens Christmas event is a event that happens once a year.
The christmas event in 2017 is the same as the christmas event in 2016, with a new furniture item called the Train Table. The train table was a 5% chance roll and a Very Rare tier item and it was also listed as one of the top rarest things with the other things being Sleigher for 1% chance, 20,000$ for 10% chance, and 5,000$ for 20% chance. You also had the option to purchase the sleigher at some point. A button would appear with the text "Or just, y'know" which would allow you to purchase the Sleigher for 2,000 R$. Upon clicking the Reroll button, the player will be given the option to purchase a Reroll for 24 R$.
The event started 12/22/2017 and ended 1/5/2018
The Christmas event in 2016 was a slightly different take on the gift system for the 2015. There was the introduction of rarities in which some items would be more rare than others and have a different tier, some of the rarest were listed to the side. 20,000$ for 10% chance and 5,000 for a 20% chance. There was also the introduction of an extremely rare and exclusive limited vehicle called the Sleigher which was obtainable at a 1% chance from the present roll, this was listed on the side bar telling you of the rarest items. Sleigher for 1% chance. You also had the option to purchase the sleigher at some point. A button would appear with the text "Or just, y'know" which would allow you to purchase the Sleigher for 1,000 R$. Owning the sleigher would make the button disappear and so would the text bringing up the chances of getting the sleigher, implying that it's not obtainable twice. The tiers are as follows: Common, Rare, Very Rare, Epic (Epic is the tier for the sleigher)
The event started 12/18/2016 and ended 1/5/2017
The Christmas 2015 event is really old and therefor not very documented. The main addition was a new menu to the side of the daily login bonus which was daily presents which allowed you to roll and recieve a random item (furniture or cash) each day. Once the present was done rolling you could either accept or re-roll for some robux to get another chance at rarer items.
The event started 12/25/2015 and ended 1/5/2016
This is the one of, if not, the oldest events in RoCitizens history. This may have also been the first RoCitizens event to ever happen. This, in fact, is so old that there is literally no known documents of the event. This may be the only place where you will even have heard of this event in your life. The Christmas 2014 event.. I don't have any documentation of it but I might get some soon to fill this in
The event started whenever and ended whenever, I don't think I'll ever be able to tell honestly
But there's a trend with ending dates so it probably ended 1/5/2015