When playing as these characters: Mario, Luigi, Link, Bill Try to hold both Left and Right buttons. The character will either always have a Slowing Down animation (Mario, Luigi), but not always. Or it will "walk" on the same place (Link, Bill). The same for walking in contact with the wall/pipe. Also (probably unrelated), if Mega Man or Bass are in contact with the wall/pipe (very close to it), attempting to go further will just move their leg one pixel, and then back (press some times the key which is relative to the wall/pipe's position and you will see). Note that it may virtually apply to all characters, but I only said what is visually noticeable.