...la laaa laaa laaa la la:
TASK: An odd number of related things (greater than 50) have been hidden horizontally, vertically and diagonally in the grid above. Each 'thing' may be a single word or consist of multiple parts (e.g. a person's full name), and is at least 4 letters in length. Your task is to find all of the hidden things, explaining their relevance to the Christmas-themed construction of this puzzle. The leftover letters should help you identify one final 'thing' that this puzzle would be incomplete without (which should hopefully become obvious once you crack what is going on here...).
Important caveat: One 5-letter thing appears backwards within the letters of one 12-letter thing found diagonally within the grid. There are no other (intentional) cases of things appearing entirely as substrings of other things in the grid, either forwards or backwards.
Text version of the wordsearch (for copy-paste purposes):
WERIUGAMTTAMOTIMABUSE ACHAMBERKCABREHTAELEZ HHRJNELLUMYRRALRILLNT SAPHILCOLLINSPANEEEOR DRKBETWEENVUIRNWNLWJE ALITUNDRAOGHNESGOHIAC RITNNACULASALUADOELYO BECRGAHDRNMGBGYODELTO KWHPUOEIOENEEKPNIEAAL CAEAUMSITYNMCEIRRPHKE ITNSOYPTLNEIRDSNOOTYP NTERNMEEANMDAAUQRAFAO OSTOANVITROLAJORDANRU OTTHAEDREERACHAPMANOL MFCJESUSCHRISTENGISGE HABEWICKSNCOSCOROBAET TRLAUNDRYKARENHAUERRP ICPROFESSIONEDARTDPTE ERCHADSMITHRCTRTRIAAR KIYESMIWRETEPYUAIARYA DAMYDOWDENCGETXMNGLLB DNADIYABYCHKOVAULROOO LNRDOOWTEELFKCIMAAURN EEPURITYREECETATUMRGU ILJEFFAGOOSDELAPRIMER FSKERMANORYBLACAILLES LOGGERHEADELHORGEVADE INOITACOVPAULGAUSTADR OGNIDDEWBLACKSCULLERY