Complex sentence: He appears slightly unstable due to what was done to him since being sent to the Attic and taunts Adelle about the technology getting out of control, he is not seen again in the later flashbacks.
Split into simpler sentences: He appears slightly unstable due to what was done to him since being sent to the Attic and taunts Adelle about the technology getting out of control. He is not seen again in the later flashbacks.