From: Mushroom Kingdom
Credits to Psycrow who found out about this (unfortuantely now patched) glitch in Super Mario Maker, Blue Television Games who showed this to me and NightYoshi370 who made this a written tutorial.
1. Make 2 clown cars.
2. Place a lava bubble in one of them
3. Place a bowser
4. Place a mushroom on the bowser
5. Place the bowser inside a clown car.
6. Make a diagonal track.
7. Copy the lava bubble from the clown car onto the track.
8. Shake the track.
9. Drag a mushroom onto the lava bubble.
10. Hit undo twice.
11. Copy bowser onto the lava bubble.
12. Hit play.
13. Hit edit
14. Drag the track elsewhere.
15. Hold the L or R button
16. Highlight where the track was.
17. Hold the ZL or ZR button.
18. Make a copy of the track.
19. Shake the copied track.
20. Drag a mushroom onto the lava bubble.
21. Hit undo twice.
22. Drag a goomba/galoomba onto the lava bubble.
23. Drag the track elsewhere.
At this point, you should have a floating bowser with an arrow on him, and a floating lava bubble with an arrow on him.
24. Erase the original trach with the lava bubble.
25. Hold the ZL or ZR button.
26. Make a copy of the bowser with a clown car.
27. Drag bowser out of the copied clown car.
28. Hit undo once
29. Drag the copied clown car elsewhere.
You should have a bowser by himself, a bowser with an arrow with a clown car, and a bowser with a clown car.
30. Drag the bowser that is in the clown car with the arrow out of the clown car.
31. Drag the bowser that is in the other clown car out of the clown car.
32. Hit undo twice.
33. Erase all of the bowsers.
34. Drag the giant clown car onto the track with the galoomba.
35. Drag it out of the track.
36. Delete all the other mess.
Congrats! You made yourself a giant clown car. Here's a video tutorial made by Blue Television Games: