In response to Siaobells answer...
Riddle 1: Try to defeat me but try in vain, when I win I end your pain.
death---correct
Riddle 2: I have two heads but one body. The more I stand, the faster I run.
hourglass---this time correct
Riddle 3: Always do I tell the truth yet cannot speak. Look at me and see what really is.
mirror---correct
Riddle 4: Name me and so shall you break me.
promise---wrong...*hint* what is golden?
Riddle 5: I will save your life but you can die from me. I will settle disputes but not with words.
drugs---wrong, secret's answer is correct...guns, swords and the like...
Riddle 6: To those within underground caves I am joy. To those fully beneath my gaze, I can be Hell.
sun---correct
Riddle 7: Here, in this place, you swallow me. Yet were I more, I could swallow you.
water---correct
Riddle 8: Two brothers we are, great burdens we bear, all day we are bitterly pressed. Yet this I will say- we are full all the day, and empty when we rest.
feet---wrong, but very close...feet when rest become empty one meh? duh?
Riddle 9: At night I come without being fetched, at day I am gone without being stolen.
darkness---wrong, secret's more close...comon, what's up there beside moon??
Total score:5/9 (same as secret leh...comeon Riddler part II comeing liao...)