Complex sentence: Treasure's founders had come from Konami where they worked on Nintendo Entertainment System games such as "Castlevania" and "Contra", but found the development environment restrictive and left on a mission to try riskier concepts and singularly focus on making "great games".
Split into simpler sentences: Treasure's founders had come from Konami, where they worked on Nintendo Entertainment System games such as "Castlevania" and "Contra". They found their development environment restrictive and left to try riskier concepts and to singularly focus on making "great games".