White Trinity is the last trinity you get, and you get it by defeating riku in your first fight w/ him in Hollow Bastion, or the second to last world. Then, you go bak to Wonderland, and navigate around lotus forest and bizzare room until you get to the bizzare room wall where there is a painting, go through the painting, and if i remember correctly, use the white trinity to get a chest w/ the lady luck