2011-12 Modified format (TCG)

The 2011-12 Modified format of the Pokémon Trading Card Game (informally called HS-on and now referred to as Standard format) was a former Standard format used for Play! Pokémon organized play and in most sanctioned tournaments worldwide from July 2011 to August 2012. It was also used in the Pokémon Trading Card Game Online.

Play period

The 2011-12 Modified format was announced on April 26, 2011, rotating out of the last sets of the Diamond & Pearl Series and the entire Platinum Series.

North America and Europe: July 1, 2011 to August 31, 2012

Rotated expansions

Diamond & Pearl Series

Platinum Series

Black Star Promos

DP Black Star Promos cards numbered DP22 and higher

Legal expansions

HeartGold & SoulSilver Series

Call of Legends Series

Call of Legends

Black & White Series

Black Star Promos

HGSS Black Star Promos cards numbered HGSS01 and higher
BW Black Star Promos cards numbered BW01 and higher

McDonald's Collection

Premier events

2011 World Championships
2011 Battle Roads Autumn
2011-2012 City Championships
2011-2012 State/Province/Territory Championships
2011-2012 Regional Championships (U.S. & Canada)
2012 Battle Roads Spring
2012 National Championships
2012 World Championships

Trivia

Bulbanews has an article related to this subject:

Play! Pokémon announces early TCG rotation to HGSS-on

This format features the first pre-Worlds rotation in the Pokémon Trading Card Game's history. This likely came about in response to the heavy controversy surrounding Black & White's first-turn rule in the previous format, with cards like Sableye creating a metagame that many players felt was too unbalanced and luck-based to be at all enjoyable.