Are Purim masks/costumes a recent thing? Personally, I find the masks and costumes worn by adults to be strange and do not in any way feel Kodesh to me. Kids dressed as Mordechai, Ester, Avraham...this is pleasant. but facial masks and strange costumes take away from joy and Kedusha in my opinion. What is the history of costumes/masks on purim and what is the in Halachic source for it? Am I correct that such masks/costumes for adults are not truly appropriate?

Masks and costumes on Purim are not a recent innovation, but a very ancient custom. It is important to note that it is not an obligatory Halachic custom, but something that many people did. On one hand, we find that it caused a big controversy in regard to the prohibition "A woman shall not wear that which pertained unto a man, neither shall a man put on a woman's garment "(Deuteronomy 22, 5), and on the other hand many reasonings and references were given over the centuries. The earliest sources I found to the costumes custom in various events is from the era of the Rishonim in the 12th century. In Sefer Yereim of Rabbi Eliezer of Mitz, one of the Baalei Hatosfot and the disciple of Rabbeinu Tam. Also in a responsa of the Rambam quoted in Sefer Maaseh Rokech of Rabbi Masud Chai Rokeach. The earliest source I found that refers explicitly to Purim costumes is from the end of the era of the Rishonim, in the Musar Sefer Even Bochen of Rabbi Klonimus B"r Klonimus of the 13th century. In the Varmaisha community Sefer Haminhagim of Rabbi Yosfa Shamesh of the 17th century there is a detailed description of the costumes custom in their community. The indication from the descriptions in the various sources is that both adults and young people used to dress up. The style of costumes ranged from a man wearing clothes of a woman to clothes of gentiles, and various masks and costumes. In the Book of Our Heritage, Rabbi Eliyahu Ki-Tov brings many reasons for the custom of masquerading on Purim. We find in the Meiri, in the Shlah and in Chayey Adam, that they vehemently decry misconduct on Purim, and that there is no mitzvah to “go crazy” on Purim. Therefore the conclusion from this is that you cannot disapprove of such an ancient Jewish custom. Yet it is very important not to cross the fine line of good taste. [המקורות בהרחבה במאמרי "תחפושות בפורים ובאירועים שונים" //www.yeshiva.org.il/midrash/shiur.asp?cat=339&id=13419&q=]