After travelling back in time late in the game, enter the sewers with a purple glowing time symbol on the floor. Use Thomas Jefferson's Diplomat ability to speak to the kid that has a piece of candy to the right. The kid will give you candy corn. Notice the mound of dirt sticking out of the sewer floor just above the kid's head. Plant the candy corn and a green sprout will grow. Return to the present and move to the right side of the neighborhood. Find the Grubbin that is watering plants near the corner of the dead end street. That Grubbin requires help to remember something. Use Thomas Jefferson's Diplomat ability, equip your party with the upgraded Hot Dog costume, the upgraded Super Hero costume, and the Teenage Wolf costume. Talk to him while wearing all three costumes to get Fertilizer from the Grubbin. Travel back in time and return to the sprout in the sewer. Use the Fertilizer on it, then return to the present. Pass through the shutter door and enter the Research Lab. Walk upstairs to the roof of the Dental Compound, then go down to find a huge tree. Use its branch to reach the center then smash the side to enter the trunk. Keep following the path up to the top of the tree, which is in space. Open the chest located there to collect the Solar System costume.