Re: Sword Oriented Martial Art
One of the nice things about the HERO System's martial arts is that they can be used to simulate just about everything.
Fencing has been published in the Ultimate Martial Artist (p.24-26), along with Kenjustsu (p.35-37) and the more general 'Weapons Combat' (p.59-60).
However, making your own martial art is pretty easy. For an armed combat style, the default weapon group becomes 'sword' (and based on your description you're talking about either a battle sword - colloquilally known as a bastard sword - or a greatsword).
The maneuver you describe (using the leading hand to grab the sword at the ricasso and stab) sounds like a Defensive Strike - sacrificing power for accuracy, and a stab threatens a longer range than a slash which translates into a higher DCV pretty well.
Grabbing the blade and swinging the pommel at the opponent is of limited use, but with the right power build you could take advantage of a feature sometimes seen on battle swords - a crossguard that tapers down into a very narrow, almost pointed end. This can be (and occasionally was) used as an improvised warhammer or pick.
The classic movie 'high guard into downward strike' makes a good Sacrifice Strike - high guard leaves you open to being stabbed, or even slashed by a faster weapon/opponent. And the good ole' 'swing for the rafters' slash could be an Offensive Strike.
Out of curiousity, are you the GM making this for your players, or a player hoping to get GM approval for this?