Complex sentence: Another demon, made by Zolgear to be his right-hand, sent to keep an eye on Mio alongside Lars, and was originally envious of the pacts that Basara has with Maria, Mio and Yuki, since they care for each other.
Split into simpler sentences: Another demon, made by Zolgear, sent to keep an eye on Mio alongside Lars. She's the right-hand of the Demon Zolgear and is originally envious of the pacts that Basara has with Maria, Mio and Yuki, since they care for each other.