Q. Why do some people hire a badchan at weddings, isn’t that prohibited?

A. The Tur (E.H. 65) defines the obligation to gladden a chosson and kallah as a “mitzvah gedola”, (it is part of the mitzvah of veahavta lereiacha kemocha), and it is achieved both by dancing for them and by saying things that will make them happy. The source is in Brachos (6b); “The reward for attending a wedding is for the words one says”, “to the chosson that bring him joy” (Rashi ibid.). Perishah (E.H. 65) adds that it is alluded in the five voices mentioned in Irmiyahu (33:11) in regards to gladdening the chosson (Brachos ibid.). It is a long standing and established tradition in some communities to hire a professional badchan to favorably achieve the above (Ramossim Tzofim, Eliahu Zuta 20 – see also Maharil on Aseres Yemey Teshuvo)

The Talmud (Taanis 22a) also relates how Eliahu indicated to Rav Beroka that only a few present in the busy marketplace of Bei Lefet, were destined to the World to Come. They included two individuals that were comedians and would cheer up those who are depressed.
As mentioned above in the prior question, Mishna Berura (560,20) quotes the opinion of the Taz that the prohibition for a person filling his mouth with laughter in this world (Brachos 31a) applies even during the compliance of a mitzva such as a wedding or Purim. As mentioned, many Poiskim explain that this applies only to total engagement in laud uncontrollable hilarity and unrestrained frivolity and not when it is done with the proper spirit of this great mitzvah. (see Peleh Yoetz, erech chosson).

Rabbi A. Bartfeld as revised by Horav Shlomo Miller shlit”a