So I have a level 36 pet (agility 286 with equipment) that I sent on a level 25 very hard mission. The first time he performed satisfactory, but the second time he failed.
I've looked at the mission guide in the forum, but can't find any reason why he would succeed, then fail.
What am I missing here?

Thanks in advance.

there is an RNG roll involved in missions, So I'd assume that the 286 might just fall into the range where it would typically get a Poor or Satisfactory completion but a particularly bad RNG roll could get a Fail.
(unfortunately we the players do not know the actual numbers involved)
Assuming the pet in question is Crimson, I'd guess that if he just had some better equips (since he currently has an epic lv15, and two rare lv20s) he'd fall at least solidly into the Satisfactory zone, (full lv25 legendary illusionist would get his agi up to 349)

Oh, I didn't think of RNG. Thanks for the explanation, that makes total sense.
Yes, I've been a bit lazy with equipping poor Crimson, so I'll have to give him some better stuff now that I've got some.
Thanks for the help :)