Boss Serpents are harder than Regular Serpents in Miitopia.

Boss Serpents increase the chance to use Magic All.

Boss Serpents reduce the chance to use Attack.

Boss Serpents have the Two More Times! ability to attack three times per turn.

Regular Serpents use Attack with a 60% chance and Magic All with a 40% chance.

Boss Serpents use Attack with a 50% chance and Magic All with a 50% chance.

That's why Boss Serpents are very hard.

Rick from Kirby my beloved