HBO's "Game of Thrones" will feature more visual effects and additional tweaks to the source material's structure during Season 2, which premieres April 1.

Based on author George R.R. Martin's second "A Song of Ice and Fire" novel "A Clash of Kings," the second season of the network's hit fantasy series required a number of changes to help preserve the tale's dramatic impact on television, according to executive producer and series co-creator D.B Weiss.

"The changes we make, taking something from one book and putting it in the middle of events from another book, are always at the service of the series as a whole -- both George's series and our series," Weiss recently told the Los Angeles Times. "Oftentimes an event from Book 2 will serve as a better end point for a character in Season 1 than it would as a starting point in Season 2.

"This year there are definitely things we took from Book 3 and pulled them back a season and there are things we hold off on introducing from Book 2 to put in a later season and there are things, regrettably, there's just no room to include at all."

Still, one aspect of the series that will not be placed on hold is visual effects, which definitely play a much bigger role this season, according to Weiss.

"I don’t have a shot count in front of me, but I know those can be deceptive," Weiss explained. "Lots of visual effects shots are fixes. And one of the great things that we’ve learned this season was how to minimize those low-value fix shots by not needing the fixes to begin with ... how to get the right blood spray that you want in production so you don’t need to add it in later.

"For every one of those you can save, it’s more money spent on a visual effects shot that people are really going to notice. ... But we have such an amazing group of visual effects artists this year that you're sometimes hard-pressed to remember what was real and what was added in later."

In fact, a pivotal visual effect sequence will be an epic battle during Episode 9, "Blackwater," which was scripted by Martin, who also penned the Season 1 episode "The Pointy End." Feature film director Neil Marshall ("The Descent," "Centurion") is helming this challenging event. Speculation about the battle's running time has already started, including one source stating that it was only 16 minutes long.

"All I can say is that if I can't quote you a number and David [Benioff] can't quote you a number about how many minutes the battle sequence is in that episode, then nobody else can either," he said. "We know there's a huge, complex battle to service and we know there's a human drama taking place over the course of the battle we need to service, and we're telling the story as effectively as we could with the resources we had, never losing sight of the people involved, which ultimately makes the battle sequence worth watching. Otherwise it's just eye candy."

"Game of Thrones" chronicles a treacherous clash among royal families to secure ultimate power of Westeros, a vast kingdom facing peril at every corner.

Season 1 of "Game of Thrones" received 13 Primetime Emmy Award nominations, including Outstanding Drama Series. It captured Emmys for Outstanding Supporting Actor in a Drama (Peter Dinklage) and Outstanding Main Title Design. Dinklage also won a Golden Globe for his performance.

In addition, the series was nominated several times during the 2011 Airlock Alpha Portal Awards, scoring wins for Best Actor/Television (Sean Bean), Best Episode/Television ("Winter is Coming") and Best Series/Television.

The series, which is also executive produced and co-created by David Benioff ("Troy," "The Kite Runner"), stars Lena Headey, Nikolaj Coster-Waldau, Emilia Clarke, Michelle Fairley, Maisie Williams, Sophie Turner, Kit Harington.

Some of Season 2's cast additions include:

--German actor Tom Wlaschiha ("Enemy at the Gates") plays the deadly assassin Jaqen H’gar, who is one of the criminals being transported along with Arya to the great ice wall.

--Nonso Anozie, a British theatre actor, is playing Xaro Xhoan Daxos, who is a Qartheen merchant-prince that offers to help Daenerys Targaryen (Emilia Clarke).

--Gemma Whelan ("The Wolfman," "Gulliver's Travels") plays Yara, the sister of Theon Greyjoy. Known as Asha in the novels, the character was renamed by producers to apparently avoid confusion with the wildling character Osha (Natalia Tena).

--Stephen Dillane ("John Adams") plays Stannis Baratheon, the hard-nosed younger brother of the late King Robert.

--Carice van Houten ("Valkyrie," "Repo Men") plays Melisandre, a sorceress tied to a mysterious religion from across the Narrow Sea.

--Liam Cunningham ("Camelot," "Outcasts") plays Davos Seaworth, whose smuggling background earned him the nickname “The Onion Knight.”

--Gwendoline Christie plays Brienne, a warrior in service of Stannis' brother Renley (Gethin Anthony).

--Natalie Dormer ("The Tudors") signed aboard the series as Margaery Tyrell.

--Robert Pugh ("Master and Commander: The Far Side of the World," "Robin Hood") is playing Craster, a wildling who lives north of the great ice wall and often assists the Night's Watch with their patrols.

--Hannah Murray (the U.K.'s "Skins") is playing one of Craster's wife-daughters, Gilly.

--Irish actor Michael McElhatton ("Masterpiece Mystery," "Fifty Dead Men Walking") is playing Roose Bolton, one of the Stark family's most feared and notorious bannermen. The Boltons are known for skinning their enemies and having a tense relationship with the Starks.

See more of Weiss' interview with the Los Angeles Times here.

View the latest trailer for "Game of Thrones" here.