Nostalgia/YMMV

• Demonic Spiders - Pretty much all of the random airship battles except the first handful fall into this category, as they're Goddamn Bats when you're fully kitted-out with the best equipment you can get for that point in the plot, and if you've just started out in that specific area? Expect quite a few surprise Game Overs. It doesn't help that the later-game ones also have more HP than many of the game's bosses...
• Game Breaker - Eddie's Overdrive and Combo Attack skills are gained near the very beginning, and can annihilate bosses in just a few rounds even quite a ways into the game. By the time it stops being as effective on bosses, you've gained your plot-unlocked ultimate attacks.