From December 26, 2018 ~ December 31, 2018, collect cross coins from Union Cross to unlock the Balloon Snowman avatar board! The Balloon Snowman (M/F) avatar part has a Rare Enemy Perk +2.

For 30 minutes each day during the following times, there will be an increased chance for rare enemies to appear! 
● 4:00 a.m. - 4:29 a.m. (PT) / 12:00 to 12:29 (UTC) 
● 10:00 a.m. - 10:29 a.m. (PT) / 18:00 to 18:29 (UTC) 
● 2:00 p.m. - 2:29 p.m. (PT) / 22:00 to 22:29 (UTC) 
● 7:00 p.m. - 7:29 p.m. (PT) / 3:00 to 3:29 (UTC) 
● 11:00 p.m. - 11:29 p.m. (PT) / 7:00 to 7:29 (UTC)

For 30 minutes each day during the following times, the Extra Hard Boss will be extra difficult and yield bonus coins! 
● 4:00 a.m. - 4:29 a.m. (PT) / 12:00 to 12:29 (UTC) 
● 10:00 a.m. - 10:29 a.m. (PT) / 18:00 to 18:29 (UTC) 
● 2:00 p.m. - 2:29 p.m. (PT) / 22:00 to 22:29 (UTC) 
● 7:00 p.m. - 7:29 p.m. (PT) / 3:00 to 3:29 (UTC) 
● 11:00 p.m. - 11:29 p.m. (PT) / 7:00 to 7:29 (UTC)

 

The raid boss seems harder than usual.  It seems like it has over 130000+ HP when you go to face it.

Yeah, they had to adjust its HP due to the recent buff cap increase. The whole idea of Union Cross quests was to make people work together; if you can't kill the thing by yourself or survive by yourself, it forces you to play with other players. (There was a time when I was strong enough that I could just go in by myself and take out the boss, but not anymore.)