This only works with joystick, but if you angle it somewhere in between down and left/right, Bernie will just slide on the ground while crouching. It’s pretty entertaining to do and can be a challenge to beat a stage just by crouch sliding.

Sliding is actually helpful especially during 1-3: it helps you dodge the last fireball you see without having to stop moving.

I saw that in your run and thought it was neat. It's faster to stay small and just walk under that fireball, but if you're going to get it, that's definitely a cool trick. (At least for any%. I don't know if getting the powerup is better for all coins.)

I haven't run All Coins since a long time, but having power up can help you getting coins, since it makes Bernie's hitbox larger. You can also use a power up to damage boost on 4-1, during the area with the 2 pipemen. With the invincibility frames, you can continue the level and grab the coins in this area, instead of waiting (you can't do the late jump, since you have several coins to grab).

Yeah, I prefer being Super for the all coins run overall because collecting coins is a lot easier with the bigger hit box (most noticeable in stages like 1-1, 1-2 and parts of 4-1) combined with the damage boosting and the fact that you can also have a backup in case you do take a hit (getting an extra apple/shroom in 3-2 is pretty easy and not a big time loss).

I also timed 1-1 both with and without getting the powerup, and I think it comes to about the same time, so I think it's worth it personally (although it does make some jumps, like the one near the end of 2-2 a bit harder).