If you are just standing there or their mob is out of control and flying off everywhere and runs to you, it's generally fine to keep going if they didn't lose many monsters and it was an accident. You can try to return them or FW if they lost more monsters than you had (like if you only had 1-3 things following you), especially if they turn around to try to get some back, but you don't really have to since it's not your fault you were just standing there. If the player just runs off, they probably don't care enough to make a big deal out of it, but try to avoid doing it again if you were moving, too (if you were just standing there, don't worry about it - it would look more like they were trying to MPK you).
It is good to apologize if they do get upset about it.
If they harass you about it afterward, you become the person who can report if you already apologized and it was an accident. They should keep better control of their monsters if they want to keep them instead of throwing them onto random players and yelling at them for just being there.
... but if you're following someone close enough that their monsters change target onto you even though they were definitely following that person, that is considered stealing monsters and is reportable on multiple offenses last I recall. It is much easier to screen shot, too.
Crashing into other players is an accident and depends on how stingy the two players are. If a lot of their monsters run onto me, I'd try to return them or FW - but I kind of wait to see what the other person does so long as I'm on a character who can live through a small wait.
As long as you hit your monsters before they lost their monsters on you it should be relatively easy to return them since you didn't hit theirs, right?
You're just not required to return them if it's their fault they lost their monsters.
Like above though, I would not take back monsters if they start hitting someone else and just move on.
I believe that's how it is more or less.
Ah... new reply.
