This patch implements some fixes to the swimming mechanics of the underwater stage, inspired by Displaced Gamers' youtube video on the subject (see link). Pressing down rapidly maxes out the turtles' downward velocity, and the game no longer carries current values into areas without current, such as the long seaweed corridor.
Database match: Teenage Mutant Ninja Turtles (USA)
Database: No-Intro: Nintendo Entertainment System (v. 20210216-231042)
File SHA-1: 89ADF2D9E453FC7FC491F968495C80C0C4A568D5
File CRC32: 83213CA0
ROM SHA-1: B239C2D48E84CA676DEE4461D4D6A1F77F34255D
ROM CRC32: EE921D8E