Ok there is the classic battle of the forms as to which jurisdiction apply
but in the case where both parties agree to a jurisdiction, then the matter is 99% of the time heard there, and most other countries court will accept this in a civil case.
If they get an order against mtgox that's just the
beginning. Even if a court is quick to grant relief against mtgox that does not mean enforcing that order will be anywhere close to easy. They could get an order today saying mtgox owes them $75,000,000 - that doesn't mean they'll ever see a dime of the money.