Clamber

You can enter a larger creature's space, to set up internal flanks by moving under, onto, or amidst the target creature. Clamber is NOT used to move through an enemy's space (you have to use the Overrun combat maneuver for that), nor can it ever affect multiple creatures. Move actions used to clamber are always at half your normal speed for the movement type you are using. This affects the whole move action, not just the squares in which you enter the creature's space. Clamber includes avoiding the attack of opportunity from the target creature, but not from other nearby creatures who also threaten you. Those creatures require a tumble check, using acrobatics, to avoid provoking from, if you wish to do so. However, the target creature of clamber only gets an attack of opportunity against you if you fail your clamber check by 5 or more (see failure). If you choose to both tumble and clamber in the same move action, your movement is only halved once for both actions (i.e. not quartered). However, difficult terrain in your path still costs twice as much movement to move into, out of your already-halved speed. The target creature must be at least 2 size categories larger than you. Note that all internal squares of a creature are considered to be threatened by that creature. If you succeed, you may move up to your speed, and position yourself anywhere inside the target creature's space, assuming you have movement enough to reach it.
Action Required:	Move action at half speed
DC of Check:	the target creature's Maneuver Defense
Modifiers to Check	You can move at full speed by increasing the DC of the check by +10. Clamber may still be performed if you are wearing medium or heavy armor, or even encumbered with a medium or heavy load. You can clamber while Prone, but doing so requires a full-round action to move 5 feet, and the DC is increased by +5.
Take 10? / Take 20?	No
Allows Assists?	{{{Assist}}}
Results of Success	You enter the creature's space and move into one of its interior squares. You cannot move to a square further away than you can reach in a single move action. You do not provoke an attack of opportunity from the target creature, though your movement might provoke from any other creatures which threaten squares you are moving through.
Consequences of Failure	If you fail, your movement ends in the first unoccupied space of your path, and you provoke an attack of opportunity from the target creature. Any remaining movement in your move action is lost.
Retry Allowed?	Requires another move action. Retrying does not negate checks which have failed.
Provokes AOO?	Only on a check that fails by 5 or more