The demon Syeonell appears in the grimoire The Book of Oberon
From The Book of Oberon, Joseph H. Peterson and Dan Harms edition:
Syeonell, magnus Comes, he appeareth like a fierce beare, & when the maister will, he appeareth like a child, & then he teacheth best all kinde of languages, & telleth where treasure is hid & hath under him 18 legions.
This demon later appears like the creature Child
Timeline of related events
1577Book of Oberon completed (lists this demon)