From the Super Mario Wiki
Triangular Blocks (also referred to as Triangle Blocks) are pink, triangle-shaped blocks with faces which are located at the bases of certain walls. They are primarily found throughout Dinosaur Land and first appear in Super Mario World.
If the Mario brothers run onto a Triangular Block, they will be able to continue their sprint by running up the wall that the block is placed against. This technique is required for getting get over tall walls that the they are unable to fly over. Yoshi is unable to use Triangular Blocks, but if he runs onto one, he will bounce high up. If a Koopa Shell hits a Triangle Block, it will also bounce up.
Triangular Blocks are also found in a few levels of World-e in Super Mario Advance 4: Super Mario Bros. 3. In addition to appearing at the bases of certain walls, Triangular blocks also appear between walls and ceilings, allowing Mario and Luigi to run up walls and onto ceilings. Only one level released outside of Japan, Slidin' the Slopes, features Triangular Blocks.
Triangular Blocks appear in three episodes of the Super Mario World cartoons. One is first featured in "Ghosts R Us", where Yoshi (who can, staying consistent with the games, only bounce on the block) briefly uses it to travel into Wizenheimer's Haunted House and save Mario, Luigi, Princess Toadstool, and Oogtar. Yoshi refers to the block as "Triangle Blockety", although the "-ety" added onto "Triangle Block" in this name may merely be a use of Yoshi's childish pronunciation on the show. During a later episode, "King Scoopa Koopa", in an attempt to escape from the Chickendactyl-turned Cave People, Mario and Princess Toadstool run up a Triangular Block leading to a Star Path. In the episode "Born to Ride", Mario, Luigi, Princess Toadstool and Yoshi used a Triangular Block to drive up the wall in their motorbikes to avoid Duke, Lulu and Rockman. Rockman attempted to drive up the wall using the block, but failed and crashed (the block was also shown to frown as soon as Rockman failed).