Nian's Hunter
Inside event cave there are Nian's that will be randomly spawned, you will need a firework to kill it, simply press space when facing the Nian, be carefull they are very agile, so act fast.
You can do group inside the event cave, but only the last hitter get the score for ranking. Do not worry getting killed inside the cave, you will not lose anything at all.

Angpao Collector
When you killed the Nian inside the cave, you will have a chance to loot an Angpao, get a group inside the event cave is better since when the Nian's died all member inside the group has a chance to loot an Angpao, everytime you get an angpao inside the cave your score will be updated.

Have Fun :)

Notes:
You can exchange angpao for fireworks, make sure you have plenty of fireworks before entering the event cave.