Finding Boom Boom
From the Super Mario Wiki
Finding Boom Boom is an official course in Course World in Super Mario Maker 2. It is a level published by NintendoAU, and was shown on the first episode of The D.I.Y. Shift. It is set in the ground theme for its main area and in the underground theme for its sub-area, as well as in the Super Mario Bros. 3 style.
The level begins with a ? Block containing a Super Mushroom, along with some Koopa Troopas, one of which Mario can kick into an ON/OFF Switch. Afterwards, Mario must enter a Warp Pipe secluded in ON/OFF blocks, then slide down a long group of slopes to reach Boom Boom. After defeating Boom Boom, Mario must enter another Warp Pipe, then move past several Fire Piranha Plants to the goal.
"Find Boom Boom's lair and defeat him to clear the course!"