Synonyms that are in the dictionary are marked in green. Synonyms that are not in the dictionary are marked in red.
Antonyms that are in the dictionary are marked in green. Antonyms that are not in the dictionary are marked in red.
It's possible that the creators thought Slappy would look too ridiculous in his standard dummy form, or thought that he wouldn't be able to move around believably during the action sequences.
Source: https://screenrant.com/goosebumps-episode-9-recap-slappy-return-reveals/