I'll be dividing this into multiple sections as this will have a lot of different boss types to find. All the same, enjoy!
Challenge Rating: Level 8 and no skills: Hard, may be doable with appropriate skills.
Recommended Skills: Ignis or any of the Ignis family of abilities, Glimmer, Punish, Spiritblade, Ki Strike, Blazing Impact, Searing Arrow
Loot: Phylactery (Raises Max HP, MP, and Magic Defense for 5 Turns, Restores HP and MP to full, and permanently increases max health and mp by ten points when used.)