Halloween, like many other words ending with 'ee', has the stress on the last syllable:
haa·luh·'ween
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Fun Halloween Events
(special pandemic edition)
ˈsoʊʃəli ˈdɪstənt
pʌmpkɪn pætʃ ˈpɪkɪŋ
'hɔːrər muːvi 'draɪv-ɪns
hɔntɪd 'kɑr wɑʃ
ˌaʊtˈdɔr vɪkˈtɔriən ˈmɔrnɪŋ fer