I'm not familiar with MSW. Basically Redshark is a free, downloadable progam available exclusively at Pokebeach.com (no this is not a plug for the site; I'm simply stating facts) designed specifically for the Pokemon TCG. Every card ever made is included in the database, and the program's layout is set up like a game play mat, complete with prizes (which are automatically doled out every time you start a new game), bench slots, a stadium slot, a supporter slot, etc.. There are also a ton of game functions that Redshark will emulate, including Rock Paper Scissors, coin flipping, etc..
Regigigas is good because of its level X, although I'm sure you knew that much. The idea is to get it out turn 2, or as soon as possible after that, and power it up with Sacrifice plus something that discards cards like Felicity's Drawing and/or Lunatone. Then you just hit consistently for either 100 via Giga Blaster or 60/80 + 20 to bench with Gigaton Punch (because you should be using that as the normal Regigigas). Palkia lv. X or Pokeblower is also usually included along with a lot of Switch cards to simultaneously allow for repeated Giga Blasters as well as take out the opponent's key Pokemon before they are powered up, or get rid of Claydol so that the discard part of Giga Blaster is more damaging. What really makes the deck powerful, however, is the ability for Regigigas to heal itself with Sacrifice. While you do give up a prize each time you use it, this does not usually matter as long as your opponent is unable to OHKO Regigigas or get more prizes off your bench, which you can prevent by keeping it low to begin with, when you use Sacrifice, or good Unown G replacements (since so much of the bench damage in this format is suddenly in the form of damage placement). The fact that Regigigas is a Basic that requires no stage 1 or 2 support except perhaps Claydol is also nice, and it means you have more room for tech cards/disruption stuff like Mesprit LA, the aforementioned Palkia lv. X, etc..