Land Under Rot

You play as a small boy that falls down a rotting tree stump to rescue your sister, but at the bottom you discover an entire world inhabited by plant organisms. You quickly realize that you will be turned into mulch in this world unless you fashion a disguise, so you place a seed on your head and go out into the land under rot. Hop on mushrooms, break bark with your hard seed head, unlock abilities and interact with the plant organisms as an equal to find the whereabouts of your sister in this cute but twisted world.