Complex sentence: Moffat also instructed Nye to come up with a monster, and Nye chose the elderly people possessed by the Eknodine, reflecting his own fear of old people as a child, but he made clear that he did not intend to make children scared of their grandparents.
Split into simpler sentences: Moffat also instructed Nye to come up with a monster, and Nye chose the elderly people possessed by the Eknodine after reflecting that there was something scary about old people as a child. However, he made clear that he was not intending to make children scared of their grandparents.