Now I know that the top platform is split and if I dissolve one half the other will move back and forth but by the time I work my way through all the other screens to get back to the bottom half, the floating panel has reappeared, trapping my ride to the trinket. What do I do?
Take the checkpoint at the bottom. Now, head to the top of the room without taking any other checkpoints. Now, get the block that breaks when you're on it. Once the moving block is on the side with the checkpoint. Run into the spikes purposefully. Wait for the moving block to reach you. Run on it. Flip down when you're above the trinket. Get it! Flip up at any time. Move on to what you're doing.