Mission Portals
OK, I think I have this figured out now:
1. you can select any one of three missions available per secret mission node
2. each of the missions has a different duration to complete (which can be reduced by as much as 50% by spending pigs)
3. each mission displays the five potential rewards available but some of them may be a wildcard (for example, it may show: Birdium / Super Rareium / Autocog / ? / ? ). However you're not guaranteed which one(s) you'll actually receive upon successful completion (see below).
4. when the mission time runs to zero, there is a "success" bar (my words, not Rovios' - not sure what it's really called) at the bottom of the screen, and based on the amount of success (which can be increased by watching a video, naturally) you can earn anywhere from one to five keys to unlock the rewards mentioned above. But the rewards are all hidden inside gift boxes, so it's a crapshoot which one(s) you'll actually unlock with the keys you've earned. So the more keys you have, the better chance you have of unlocking the gift boxes you want.
My assumption (but I haven't tried this yet) is that the more TFs you have participating on a given mission, the higher your success bar will be, and the more keys you'll get. But you need to unlock an additional slot to do so.
Also, it looks like it costs 200 gems to unlock an additional TF slot (at least it does in the node I'm currently looking at, the one on the right side of the Island) - but I have no idea if this is a permanent unlock, or if it only unlocks the slot for the one mission. Would be good if someone who knows the answer to this can clarify?