I haven't actually played this yet, our lass has been playing and says she is stuck on the final boss, please could you give me some clues on how to beat it before she drives me insane

Stock up on red potion if you've fused that kinstone yet.

In the first form, blow the shadows away with the gust jar and then hit the eyes around her with your sword. A eye in the middle will open, and hit that.

In the second form use arrows to overturn the balls surrounding Vati. Your objective is to find the 4 red ones and make copies of your self to hit them at the same time with your sword.

In the third form, flip the srm with the Cane. Then, turn minish and enter. There will be tiny monsters. Kill the one that looks different with your sword. After, do the same with the other arm. (eqip lantern to see in the dark.) Turn big, and when her 4 eyes fire beams, defleact them by doing a spin attack with copies made of yourself.

Tried my best to explian.

and after you deflect the shots don't forget to go up and damage vatti (of course)

If she's stuck on the second form and needs health, avoid all the attacks and break the purple spiky things. Usually, they have arrows, but they occasionally have hearts.

thats cool.