Mario tends to interact with the bottom of hanging vines strangely.
In 12-1 hold Run and Left while attached to the vine in this position, press jump to consistently attach below the lower vine.
Pressing Up in this state nudges Mario further down, and Down nudges him back up - but he cannot climb the vine. Jumping detaches as normal.
In 12-1 on this small vine at the top, Mario can clip into the pipe and get stuck by pressing Down then Jump.
Version: 2.0.4
Mario tends to interact with the bottom of hanging vines strangely. In 12-1 hold Run and Left while attached to the vine in this position, press jump to consistently attach below the lower vine. Pressing Up in this state nudges Mario further down, and Down nudges him back up - but he cannot climb the vine. Jumping detaches as normal.
In 12-1 on this small vine at the top, Mario can clip into the pipe and get stuck by pressing Down then Jump.