Before diving into the Soul of Darkness mod, ensure you have:
Soul of Darkness is now available on DSiWare in the US, at only 500 points: http://j.mp/bwdNfK Coming soon in Europe. YouTube·Gameloft Soul of Darkness | Nintendo DSiWare | Games soul of darkness ds rom new
You want a complete story, stable saving, or more than 1 hour of gameplay. Go play Castlevania: Dawn of Sorrow instead—it does everything this game attempts, but professionally. Before diving into the Soul of Darkness mod,
Soul of Darkness is linear but has backtracking elements. Here is the critical path. soul of darkness ds rom new