Whitsun, also called Whit Sunday and Pentecost, is the Sunday 49 days after the Christian festival of Easter and in the Gregorian calendar it falls on a date between 10 May and 13 June. What pagan or folk customs or beliefs have accreted to the Christian celebration on this day, or were replaced by it, or are otherwise related to it?
Pentacost is the indwelling of the Holy Spirit into the disciples of Christ following the ascension of Jesus Christ into Heaven. It's also the Jewish festival of Shavuoth per the Oxford dictionary. Here's an excellent article tying its roots to Jewish harvest festivals at which time many people became Christians following the indwelling of the Holy Spirit. https://www.christianity.com/jesus/early-church-history/pentecost/where-did-pentecost-come-from.html It seems to be tied to Jewish holidays and traditions instead of anything pagan. Here's another article about the origin being the Jewish feast day for the firstfruits of the wheat harvest: https://www.britannica.com/topic/Pentecost-Christianity . Prior to Jesus Christ's ascension, baptism was by water as a symbol of cleanliness. After the resurrection and ascension of Jesus Christ, baptism into Christianity was with the fire of the Holy Spirit. Here are two explanations of this Baptism by the Holy Spirit: https://www.desiringgod.org/interviews/what-is-the-baptism-of-the-holy-spirit and https://www.radiant.church/foundations-of-faith-blog/part-10?gclid=EAIaIQobChMIy7-JpMaK6AIVURh9Ch10NAkLEAAYASAAEgItufD_BwE .