From the Super Mario Wiki
“Ah! I am surprised you are finding me! I am called Welderberg! I am the iron man of the forging of pipes! Have you ever thought, "Ah, it is taking so long to get around town!" Yah, me too! And so it is my life's work to make the pipes for the transportation! I have inspected here, yah... I am thinking I can make the pipe leading to Flipside. What do you think of this? You are covering cost of materials and labor, yah? You are looking not very rich... How is 300 coins? Are we having the deal?”
Welderberg is an odd hairy creature in the third dimension of Flopside in Super Paper Mario. He seems to be able to flip dimensions, and make gateways through them, and is also skilled at making Warp Pipes in a few seconds. Welderberg can make a pipe from Flipside to Flopside for 300 coins, as well as pipes between the B2 and second floors of both towns for 100 coins each.
"That's Welderberg... Give this pipe maker coins and he'll dig pipes for you... He might not look like much, but he's a master at his specialized craft... If you've got the coins to spare, you should have him dig you a pipe..."
 Names in Other Languages