Bzzaps. When you have to fight five of them... :( And they're attacks are powerful AND hard to dodge. Also Amazy Dayzees if they attack. Luckily they usually don't, but one time it attacked twice on me. That's 38 damage if you guard, 40 if you don't. And their strange timing makes it difficult to superguard.
There are too many annoying enemies to count, but most of them have been mentioned. Those that haven't include all versions of pokeys (they don't leave me alone!) and the area (not a bad guy, but whatever) in TTYD in chapter... 4? The one with Doopliss. Getting back to the town alive is a challenge (until I spam Doopliss with attacks to build up my star meter!). Unusually, gusty glade (a similar area) was easy.
Destruction isn't supposed to make sense! It's only fun when it's senseless! ~ Kefka, Dissidia Final Fantasy.