https://github.com/luminoray/Tomb-Owl-Weed/blob/dev/src/Actors/Tumbleweed.gd#L11...
In line 117 of the weed's code I added this RNG check that runs every frame that the weed is on the floor. When the check passes, I simply set the vertical velocity to -60, making it bounce a little. Since I stored the capacity to jump in a separate variable, these little bounces don't interfere if you wanted to jump, and a bounce happened to take place just before, similar to how the boot works in Mario 3 where you can jump even if its currently bouncing.
For the color changes, I actually cheated quite a bit for this one haha. The whole game is actually in grayscale, I couldnt find the proper way to do it in time, so the shortcut I took was to add a UI node, with a ColorRect covering the whole screen. I then turned it into a Shader which multiplies its own color value with that of what's behind it, basically coloring the whole scene. Since this was obstructing the whole scene however, it made it impossible to click on things, which is why I have it removed on game over.