Sneak attack, if trying to sneak on someone, uses Stealth skill + Mind stat (rolling 2d6) and foes roll Mind stat + any attributes enchanching sense which can apply to task detect sneaker. If succesful defender cannot use defense roll at all resist the attack (so automatic hit). For attacking with grapple you use your attack combat value + flexible attribute ranks and roll 2d6 (this is ofc when you are not sneak attacking succesfully). Once grappled you can do damage on foe if you want and foe can escape with Athletics + Body roll (+ any ranks in flexible as it helps escape from grapples as well), which is resisted with your grapple attack modifier in a contested roll.