1) Do cards that have give the ability to negate effects by destruction or commiting to the opponent are they considered to be commiting or destruction from the player controling the card?

Example: If my opponent activates Stand Off and I choose to negate its effect, is it commited by the effect controled by my opponent.

2) Is Mulliganing before or after the game starts, in other words can I react to my opponent removing the cards from play when they Mulligan?

Thanks.

Cards that are committed as part of a cost due to an effect do not trigger the ability on the card. In your case Torn Hero would not be able to activate since you used it as a cost to negate Stand Off's effect. Previous ruling here at www.fantasyflightgames.com/edge_foros_discusion.asp There is a more detailed answer, but I can't find it at this time.

As to the second question, mulligans happen before the first turn begins; no abilities may be played due to a mulligan.