Time Machine

Calvin's cardboard Time Machine was originally built for travelling to any point in the past, present, or future— used mainly for Calvin's get-rich-quick schemes and attempts at avoiding homework assignments. However, during the "Dimension" saga, the Time Machine somehow begins transporting Calvin and Hobbes into alternate dimensions instead of time periods; it is later suggested by Galaxoid and Nebular that this is because the box faces down and the machine miscalculates, as opposed to when the box top faces upward and works properly. (Shadow the Hedgehog later divulges that this was never the case; an unknown enemy has evidently been altering the functions of the Time Machine, as well as its successors, all along.)

INITIAL CROSSOVERS
The Time Machine first sits in Calvin's room while he gripes about his parents' disbelief of his latest time-traveling endeavor; Calvin first considers throwing the Time Machine away, but as Hobbes teases him, they begin arguing and fighting, rolling on the floor and eventually landing inside the box, still throwing punches at each other. Soon the box is upside-down, and suddenly it activates and sends both Calvin and Hobbes to Leaf Forest, an area in Sonic's dimension— though they initially believe that they simply traveled to a different time period. As events carry on, the Time Machine is later stolen by Doctor Eggman.

HUNT FOR THE CHAOS EMERALDS
Doctor Eggman uses the Time Machine to travel through the alternate dimensions, so that he may collect the now-missing chaos emeralds; he first uses the box to travel to Zim's dimension, and then to Frogger's dimension later on. He also begins harnessing the Time Machine's energy to power his vessels, so that they may travel through dimensions also, as demonstrated by the Doctor's Bomber Ship following the Skirmish in Swampy's Lair. As the hunt carries on, the Doctor continually uses the Time Machine to pursue the alliance, eventually catching up with them at the Valley of Bowser. In the end, the box is never recovered, so Calvin creates the "Time Machine 2," which allows everyone to return to their home dimensions.

SEARCH FOR THE SACRED ELEMENTS
As Calvin and Hobbes contemplate the idea of visiting Sonic and the rest of the group again, Hobbes points out that the "Time Machine 2" was destroyed after they returned home (so as to prevent it falling into the wrong hands, as the first Time Machine did), but Calvin states that they can simply make another one. Using another box and labeling it "Time Machine 3," he and Hobbes travel back to Leaf Forest, but find no one there; Calvin then decides to change the coordinates to Sonic's current location, and the box takes them to the Icecaps, where the group is battling Mr. D over a "fire element." Calvin, Hobbes, and Sonic come up with a plan to power the "Time Machine 3" with a chaos emerald, and they speed down a snowy hillside and ram into Mr. D, knocking him backward into the water. However, as he reemerges and prepares to destroy everyone with the fire element, the group escapes via Dib's wristwatch, and the box is left behind (perhaps destroyed).

After the entire mission is over, Calvin borrows a cardboard box from Professor Membrane and creates yet another Time Machine, this time labeled, "HOW MANY TIMES ARE WE GOING TO MAKE THIS THING?" The box transports everyone to the Mushroom Kingdom first, so that they may help Princess Peach rebuild what was lost, and then sends them all home once more.