What do the mission requirements mean? Some are clear, obviously. But what do 'adept' and 'sturdy' mean? Pets with high dexterity? And sturdy, pets with a lot of health?

Is there some guide that explains this, and how much of each is necessary to complete a mission? E.g. if the 'medium' quest requires min. lev 15 'adept' pet, how high should their agility be to succeed? I found some guides, but they basically just repeat the instructions 'choose the correct pet'.

My level 18 pet, with Dexterity 46, failed this quest, and my level 20 pet with Dexterity over 80 did 'poorly'. It's a bit annoying, if the mission that takes 2 hours fails or doesn't get proper reward and I have no idea why.

Or is it completely random, if they do well, poorly, or fail?

When you go to accept a mission, look in the upper left corner of the popup box. It should say Emphasized Statistic: _____. For instance, I'm looking at one now that says "adept" in the objective description, but Dexterity for the emphasized stat.

It's definitely not random. I don't know exactly the cutoffs for success/failure based on stats, unfortunately. But every mission should say the stat needed in the upper left, and knowing that'll at least give you a better chance to succeed.

I see. I'll try again and see if I can figure out the rules for this. Thanks for help! :)