Jesus mentioned satan at least 15 times and taught the existence of demons.

          Jesus cast demons out of people, in Matthew 15:22-28 And behold, a woman of Canaan came from that region and cried out to Him, saying, “Have mercy on me, O Lord, Son of David! My daughter is severely demon-possessed.”
But He answered her not a word.
And His disciples came and urged Him, saying, “Send her away, for she cries out after us.”
But He answered and said, “I was not sent except to the lost sheep of the house of Israel.”
Then she came and worshiped Him, saying, “Lord, help me!”
But He answered and said, “It is not good to take the children’s bread and throw it to the little dogs.”
And she said, “Yes, Lord, yet even the little dogs eat the crumbs which fall from their masters’ table.”
Then Jesus answered and said to her, “O woman, great is your faith! Let it be to you as you desire.” And her daughter was healed from that very hour.