I went to do what you said for Marin's Challenge but I don't seem to have that as an option. When I talk to Marin the game specifically says that I can't bring Rinny. Talking to Pixie with Rinny with me also doesn't seem to do anything
Thanks for the replies to the various comments I made, always nice to see a dev answer questions and all that themselves. Since it's not really how the game is supposed to work, I don't expect exact quest markers, but in cases like I've often had it just can get really hard to actually figure out where to go. Sometimes it's just raw luck. I don't expect nor want you to have direct instructions but more hints for the more vague missions would be nice, even if you have to look for them. There'd probably be a lot less google searches about this game then.