James some of my personal favorite mechanics in TTB would be
Magic - magic and manifested powers are so interchangeable and mutable you can make almost anything. With GM finesse your able to come up with some crazy powers ( my personal favorite i made was a Mind control character that had some stipulations before he could cast the spell such as he has to introduce himself by full name and shake their hand.)
The setting- As a long time malifaux player i love the dark gritty feel of malifaux with the steam Victorian style but with enough magic you can basically explain anything into your game.
Destiny- The destiny mechanic works great and really make me think as a gm. As players make their character they flip 5 cards these give you stats and info about the character, but this also gives you their fate. As a gm you have to try and connect these fates to your story witch i find helps me make a better fuller story that my players enjoy more because it has its spot light moments for each of them.Think about your best and worst RP moments..they all have that epic spot were it was allabout you..and TTB has that built in.