Valentine's Event 2020
The Valentine's Event 2020 started Fabruary 09th and lasted till the 14th!
During this time, users were able to obtain Sweet Hearts and send out Valentine's Cards to other users.
Every user who sent out one card to three different users were able to obtain a brand new Event Pokémon on February 15th.
The more Valentine's Cards you sent out, the higher were your chance of receive a Shiny Version of the mentioned new Event Pokémon.
Every Valentine's Card cost 50 Sweet Hearts each to send. Granted the user hadn't put you on their blocklist, you would be able to send them to any user. You also have the option of attaching a message or anonymously sending the Card, though neither of the two are required.
Once obtained, they could only be used to send Valentine's Cards to other users.