re: Sierra's array
I do not think Sierra's devices in her array are very balanced. While I applaud Rystil's ability to use the rules in interesting ways, I feel overall the character's array is not balanced at all.
Indeed some of the abilities seem to be Game/Plotbreakers and would make many a GM work harder then they should simply to keep up with the character's abilities. In addition I am worried about fellow players feeling overshadowed, overpowered and unneeded.
Ah, but it's all in how it's used, isn't it? I've tried pretty hard to keep some rather sizable gaps in Sierra's capabilities, and, importantly, the new stuff is pretty much all there because people asked Sierra to do it because no one could handle that task. It's the weird thing about a living world--you can get very different teams, and that changes the way things work. Fortunately, Sierra being flighty is the perfect excuse to be erratic about which alts to use.
For example, take the Ring of Antaeus. I created that particularly because Salix had needed a tank for his adventure, and we had none available. Sierra will use it as a last resort if she must and nobody is around to tank, but she finds it boring, so she will almost never use the ring, and especially not if we already have a tank around. She's still not a better tank than, say, Paladin, who heals himself instead of taking damage from physical attacks. And it's easy to disarm and stops her from using her usual mode of transportation, flight (plus you get her off the ground and it's not working much anyway). I wanted the ring to make it easy to eliminate if the GM wants to do so as well as because it makes a whole lot of sense to me for a Mystic character to gain new and different uses for her powers whenever she finds a cool new magic item. It's a lot like what you see in the comics, where the BBEG or hero Mystic finds the X of the Great Wizard Y and now can do something awesome and new.
Another example, the Mastery of Shaping may seem a lot like the main, but people in Iridium Con made her use Extra Effort a whole bunch to extend herself and do slightly different transmutations than Human to Animal (disguises for Gun Monkey, etc). Thus, I thought that first of all, it would be better to add it if people wanted me to use it so much, and second, it seemed natural for the character to gain that as she grew in use of her main power in wider applications.
Diamond of Eris started out as a Teleport (by popular demand--and people always seem to be happy for her to have it), but I have a personal fear of messing up a game with a Teleport that goes too far and is available at any time, so I made it an easy-to-get-rid-of Device for that reason, so the GM can get rid of it if Teleport is inappropriate (there's even a note to that effect in the character sheet). Also, it seemed appropriate. Then I had more points to spend, so I also wanted to add some party protection to it. Most of you probably already know this, but Deflect is actually not that good--it's a fool's bet because while you think it gives you a 50/50 to beat the opponent of equal skill level, you actually have a much much lower chance because you have to take into account that the opponent already beat the Defense of the target, so they always roll high.
Etc for the others, but not much time right now. Honestly, I can point out characters all around that could have these same questions asked about them, but I won't because they've all worked fine because the players handle their characters well and try to help make the game more fun instead of less. Sierra has just been made prominent and singled out by the fact that I felt like talking about it just because I have fun talking about rules and mechanics and stuff.