The Trampoline is a starting object in Super Mario Maker. It may be turned on its side, or upright. If upright, it can be picked up and carried in any skin but SMB. These things are used quite a lot in Auto-Mario levels, to move Mario around by firing the sideways Trampolines from Cannons. Jumping as Mario is hopping off the Trampoline makes the jump much higher, similarly to high-jumping on an enemy.
Kicking the Trampoline upward can halt a Thwomp as it falls.