The poster is from a haredi forum saying:
Before you celebrate Sylvester / New Year’s Eve
Sylvester was a Christian pope who killed thousands of Jews.
On this day, Christians went out to celebrate the pogroms against the Jews and those Jews who were still around were killed too.
They burnt our ancestors with boiling hot oil. In addition other kinds of torture are listed on the poster.
If the day was called Hitler instead of Sylvester, would you still celebrate it ?