In Grubbins on Ice, how do I win the final battle against Araxia and Big Bones?

I'm at what I'm pretty sure is the final battle of Costume Quest but it seems impossible, for a number of reasons:

• I'm up against 2 bosses simultaneously, with 4000 HP each.
• Araxia can apparently decide to become invulnerable for several turns.
• While Araxia merely hits hard, Big Bones hits like a truck, bringing the entire party down to critical levels in one attack.
• Taking Big Bones out first doesn't seem to be possible because he can't be harmed, not even with area effects.

How do I beat this thing?

Araxia's the only one you can harm, so ignore Big Bones. When Araxia's flying and invulnerable, hitting him will knock him back - this is important. Winning this fight hinges on pushing him into Big Bones' candy stream.

I found this strategy/build that will probably be helpful:

• Attack costume - strongest attack stamp (Skeleton of the Wolf or such).
• Yeti costume - strongest poison stamp.
• Healer costume - Multi-Wing Bat stamp (full party regen).

With the above combo I attacked Araxia. After a few rounds of hitting him he will have candy fed to Big Bones, which will cause him to attack. You need to have the Yeti's shield up to avoid major damage. The damage increases every time Big Bones attacks, so you will be wiped out in a long battle no matter what.

(This strategy goes on to mention a bunch of things that I already said, but you can feel free to read it if you want the full picture :) )

Ok, I have managed to do it with following set up:
- Unicorn with Vegetarian Witch's brew stamp (poison),
- Yeti with Headless Vampire Bat stamp (big heal),
- Statue with Multi-Winged Vampire Bat stamp (heal all).

The strategy is following.

1. Passive healing should be sufficient and if accidentally someone dies just resurrect with Unicorn.
2. Give priority to pushing Crow back instead of healing/shielding, if it falls on Big bones face he will not attack that turn.
3. Save up Yeti shield for when Big Bones stands up as it lasts only one turn.

Crow has to fall on Big bones face 3 times to win the battle, no need to take away 4000HP.