How do I get the second black coin in world 1-4?

Spin Jump: To make your Mario spin in mid-air tap the screen, hold it, and then tap again.

So it would go like this:

Hold in the jump after the last dry bones.

Collect coins before the black coin.

Tap the screen quickly after releasing it to spin and grab the black one.

Since you didn't ask "How do I get the second black coin in world 1-4 as Mario", the answer is simply:

Play as a character that has a higher overall jump than Mario:

• Luigi, as he can simply jump higher than Mario.
• Any color Yoshi, as they can flutter jump to the coin.
• Daisy, as she can double jump.

For with Mario -- A trick that takes it from needing super perfect timing, to just a little timing:

You're on the right track with just getting really good spacing and timing, and adding an air-spin after springing off that last drybones. This can work, but needs almost impossible spacing and timing.

To make getting the coin manageable -- here's the trick:

Doing a mid-air spin in the air, before springing off an enemy, (the last drybones in this case) adds just a little more oomph to the spring off the enemy.

It still needs some finesse, but now I can get it most times, instead of the super perfect timing and such that I needed before adding the extra air-spin before springing off the last drybones.

With this way also -- I don't think I worry about springing on all the drybones, but at least off the 2nd and 3rd. I don't know if this matters either -- but I start from under the question blocks, not above. I feel like this process is most manageable, and maybe coming from the lower ground makes less chance of missing the coin by bouncing off the cieling when the spring off the last drybones is a lil high.