Complex sentence: In Phantasia, he has changed his appearance to a small, cute fairy being guarded by a Seraphim, but is still powerful nonetheless, almost impervious to damage from physical weapons and impossible to harm from various elements.
Split into simpler sentences: In Phantasia, he has changed his appearance to a small fairy-being guarded by a Seraphim. Nevertheless, he is still quite powerful, being almost impervious to damage from physical weapons and impossible to harm from various elements.