Complex sentence: To promote the USA release of The Necromancer Random House released an online game, "The Quest for the Codex" players were presented with a grid containing numbered squares and had to click on the squares to uncover hidden rewards, playing pieces and mini-games.
Split into simpler sentences: To promote the USA release of "The Necromancer", Random House released an online game called "The Quest for the Codex". Players were presented with a grid containing numbered squares and had to click on the squares to uncover hidden rewards, playing pieces and mini-games.