ya dude, no need to spam.
just grind and get yourself overleveled. Like around level 15 should be enough to overpower the boss.
the most powerful move you can use is Double Arrow, if you're faster and lucky enough you can STUN the boss.
when the minions appear, you can decide for yourself whether to take out the minions first or the boss first. But keep in mind that the boss sometimes would weaken the minions to heal (which could work to your advantage).
also notice when the boss dives in,you will get transformed back to your human form if you were a cat.Maybe it's a good idea to Guard after the boss dives in to reduce the damage taken and you can heal mana while you're at it.
additionally, you can steal the enemies' OFFENSE buff, put them to sleep, etc.Don't forget healing potions as well.