 An expansion to the game , entitled " Wrath of the Lamb " , was released through Steam on May 28 , 2012 . McMillen was inspired to create the expansion not only due to the success of the base game , but because his wife Danielle had fully completed the base game , the first game he had written in which she had shown significant interest . The expansion adds 70 % more content to the original , and contains more than 10 bosses , over 100 items , over 40 unlocks , two additional endings , and two additional optional levels . This expansion added new " alternate " floors , which can replace the normal floors , creating an alternate route through the game . These floors contain harder enemies , and a different set of bosses . Other features include a new item type , Trinkets , which have a variety of passive or triggered effects when carried , as well as new room types . McMillen had plans to release a second expansion beyond " Wrath of the Lamb " , but was constrained by the limits of Flash at this point . 
