First off, as a creative person I love the choice that synthesist gives, so I apologize in advance for any ruffled feathers. Please keep comments relevant and constructive.
Down to business.
The idea started as a master CMB character but spiraled off into this idea...
Synthesist, quadraped, flight (eventually to 100ft + supernatural), rake, Death from above feat, Improved grapple, Pincers (+2 grapple (not just to pincer attacks as worded)) Grab - bite (+4 grapple (not just to bite grapple as worded)) + 2 strength evolution, large, Ant haul (if encumbrance is an issue), bull strength, enlarge person, etc etc
I'm not 100% sure how grapple works. On the initial grapple if you succeed do you get a grapple action (move damage etc) or do you only apply grappled until your next turn?
If you only apply grappled on first grapple I would take a level of maneuver master monk so that I could get two maneuvers (a full-attack action which works with pounce) after the pounce so the following would be the same (if it's possible).
The idea is to float into the air then pounce (with death from above +5 to attack) to grapple. Once once grappled fly straight up into the air as a move action after continuing the grapple.
You can move both yourself and your target up to half your speed. At the end of your movement, you can place your target in any square adjacent to you. If you attempt to place your foe in a hazardous location, such as in a wall of fire or over a pit, the target receives a free attempt to break your grapple with a +4 bonus.
If i try to release it mid air it can try to break free with a +4 bonus, but who cares either way its falling 50+ ft. With the level in maneuver master monk that's twice per round(after the first) that I can attempt to continue the grapple and fly higher up until its guaranteed insta-win.
In smaller or enclosed areas you could still use a similar trick to sprint ahead, grapple one of the enemies, and use the move action to drag them back to your party to disassemble.
So is this breaking some rules?
Also another synthesist build that grabbed my attention was based on the shadow evolutions
In any condition of illumination other than bright light, the eidolon disappears into the shadows, giving it concealment (20% miss chance). If it has the shadow form evolution, it instead gains total concealment (50% miss chance). The eidolon can suspend or resume this ability as a free action.
The eidolon's body becomes shadowy and more indistinct. This shadow form grants the eidolon constant concealment (20% miss chance), and its melee attacks affect incorporeal creatures as if it had the ghost touch weapon property. The eidolon's melee attacks deal only half damage to corporeal creatures.
Does this mean with 1 level of synthesist (with extra evolutions feat) I could have permanent and at will invisibility (total concealment) in any condition of light other than bright light?