Focus Strike

After receiving instruction from an ancient, elven master and training your body, you have learned how to concentrate your energy into a single, decisive blow. As an Action, you may choose to launch a single unarmed attack at one creature. This focused strike acts as an Unarmed Strike and draws upon your energy, achieving the following effects:

• For every Ki point you choose to spend, increase the damage of your Unarmed Strike by 1d6. 
• Upon being hit, the creature must make a STR saving throw equal to your Ki save DC or be pushed 10 ft. for every Ki point spent. This effect does not work on creatures more than one size category above you (e.g., a Huge creature hit by a Medium creature).

A particularly well-struck blow proves to be invigorating. Whenever you land a critical hit using this attack, roll 1d20, and if you roll a 10 or higher, restore all your Ki points.