So, I just recorded these videos for the King Dice. Sadly, the Switch only records the last 30 seconds, so the fights will be incomplete. The fights are in Expert mode.
For my weapon, I only use the Roundabout, and for my charm, I use the Dash Bomb. And I use Super 1.
You first need to learn how to hit the dice. I need Space 3, Space 5, and Space 7. I can get the dice to hit those spaces 90% of the time. Very easy, you just need to jump one number after the number you want. If the dice rolls as 1, 2, 3, 1, 2, 3 and you want a 3, you need to jump on 1 and then parry when you see the 3.
So, for the first boss (Cigar). Very easy to avoid the fireballs. Just keep shooting backwards. The Roundabout will hit the boss. When he turns into ashes, just Dash Bomb the floating cigarettes. Use the Super when the cigar is emerging from the ashes.
Next boss (rabbit). Just get on top of the card and keep shooting in any direction; the roundabout will hit the rabbit no matter which direction you shoot. It has two attacks: circle of skulls and some crystals with shapes. For the circle of skulls, just dash bomb through them to the left. For the crystals, you will hear a magical jingle/sound before the attack, so you can prepare to parry the pink figure. Just pay attention; when you hear that magical jingle, prepare to parry. Use the Super only when you are inside the circle of skulls, and only at the beginning of the attack (when the circle is bigger) so you have time to escape with a dash bomb.
And for the last boss, we need to hit Space 7 (roulette wheel). Very easy. You don't even need to jump at all. Just keep shooting the Roundabout in any direction. Dash bomb when the Roulette runs in your direction. When she shoots some balls in the air, stay still, shooting the roundabout. When the balls are about to drop in your position, dash bomb in the opposite direction. Use the Super only when the Roulette is doing that attack.
Disclaimer: I had 4 hearts on the rabbit boss and 5 hearts in the roulette boss because randomly, those spaces had hearts on them on that particular run. I didn't use the Twin Hearts charm (the Dash Bomb is more valuable on those bosses than the Twin Hearts charm).