While I love Nu and the save points, I'm not a big fan of them as enemies, so I have to go with the scouts. Simple, effective design tells you everything you need to know: they're eyeballs with bat wings, so you know they're not good and they're color coded with their own weakness, forcing you to keep a varied team when you face them. They're not the strongest, or the coolest, or the most memorable, but they're extremely well thought out and, in my opinion, a perfect example of a Chrono Trigger monster.