Very fun addition, and definitely more difficult. The slow falling did not work for me, and despite having some trouble, I was able to make it past the slow falling section and beat the game without it. (Is pressing T supposed to warp you to the credits?)
I understand the problem with the slow fall, try activating it when the character is already falling. If you activate it during the jump, it won't work (I'll make an adjustment after the jam so that it activates at least at the end of the jump before the fall to avoid problems).
I'm glad you liked the game (the T key function was a test that I ended up forgetting to remove when uploading the game to the game jam, hahah).