Attacked randomly

[Niwashi]

those with a red icon, which are aggressive and will attack you as long as your level is not 10 or more above theirs

Minor correction, that should say "more than 10" instead of "10 or more". With a ten level difference, they'll still attack. With an eleven level difference, they won't.

If you are in a group, then monsters will be linked, which can be seen as a line connecting monsters when you target them.

Mobs can be linked when you're solo, too. (Maybe it occurs more often if you're in a group, though. I'm not sure. I'd always thought it was a static rule that certain mobs would always be linked and others never would. But I haven't really looked into it as there isn't very much content that I'll sometimes do solo and other times in a group, so I may just have not noticed the differences.)

When the worst I could do was knit them a very itchy sweater.

LOL (literally)