What's up with these seemingly random uber monsters that come out though? Twice I've fought monsters that killed me in like 1 or 2 hits. Once on the first temp island and another at the shrine. --- The King of Kings http://img18.imageshack.us/img18/9971/744sptp062727c1tyrekeem.jpg
Those are King monsters. They have a much higher level than their peon counterparts and can still be tamed. Plus they do better farm work. --- "You're right. And when you're right, you're right. And you, you're always right!"
There are also monsters you cannot damage due to plot. The little tiny spirit things, usually.
Technically the red core is a missable item, but it's kinda right in front of you when it's time to pick it up.
Also, there are thing not technically missable but way to optimize your friendship gaining:
1. Seek out king gates (white, no monsters) in earth upper floors. If you get a goblin king, tame him, He does pom poms and components for rattatouile, both are needed for friendships.
2. Practice catch-and-release with monster boxes, They give you a gem the day after they are captured, then none for like four days. So, if you want to gems to give to a certain girl, your can build up a pile. by catching, next day harvest(monster cookies required), then next day release and capture new.