Mission 14: The Voice of the H.I.V.E.
This is a set of training missions - in other words its impossible to fail these missions. They exist purely to give you a chance to gather some bonus XP for your recruited character, so its worth planning who you want to beef up from the built-in characters beforehand.
Remember that any one character can only go on one training mission out of this set.
Once you've decided who you're going to train, bear the following points in mind as to which mission you take them on.
Training Run 1 - The Queen of Tarts
Marla's slightly skewed re-telling of some earlier missions and how she defeated the Queen in the first story arc. The first three sub-missions in here are tightly time-limited, so slow characters (King Zero and Chaos) are at a disadvantage. The final showdown is vs. the Queen and her radiation gun, so Miss Amazing is best left out of this one if you choose her.
Training Run 2 - Classic Arcade Games
In the first sub-mission (the Pac Man level) the Tart robots respawn, so its more important to be able to cover the distance than to fight them.
Both missions involve fighting opponents who are vulnerable to heat and cold, resistant to crushing and mental attacks, and rely purely on crushing melee attacks, so Miss Amazing is almost ideal (heatvision, flight and complete defence vs crushing), with Devil Doll a close second.
Training Run 3 - Space Aliens
A fantasy of Marla's about rescuing a handsome scientist from aliens.
The main failure here will e with an exclusive melee character against the Alien Champion at the end - his use of FFX's Nuclear Stockpile power makes him pretty tricky for those without decent ranged attacks (and this includes Devil Doll with her short-range abilities).