Okay, so here's the strategy I've devised for taking down all three forms of Chantelise's final boss. I've included Shadow Elise (not part of my original question) because it's technically part of the final battle. By the time I beat this boss battle, I had 230 health, but I think I could surive with 150.
I assume we're in Story Mode, where you can change equipment mid-battle, but the equipment I list at the beginning of each form should work fine for dealing with the battle in Practice Mode.
Form #1 -- Shadow Elise (The Silhouette)
- Magic Crystal
- Three Magic Charms (In my case, Miracle Charm (from 5-1's treasure) and 2 Hallowed charms)
As it's fairly easy to avoid Shadow Elise's physical attacks, even when there are two of them at once, I focused my equipment towards nullifying the magical damage I could sustain as much as possible.
My approach for this battle is to wait until there are four gems of a single type on the field, and then scoop up all four and summon a spirit(ideally water or wind, since both can cast spells that restrict the opponent's movement, allowing you to wallop on your opponent with your blade). The magic crystal item speeds up your spell casting rate enough so that you can easily call out multiple spirit summons at once; as a result, when the battle gets more chaotic and gems begin to fly everywhere, look for sets of four and use them to cast as many spirits as you can. The spirits will take care of targeting your enemy; simply wait for Shadow Elise to get frozen or caught in a tornado before rushing in and attacking. Ideally, if you summon enough spirits, the water spirits should take care of healing for you, but if you ever fall down to around 100 health, I would recommend looking for three water gems to cast a quick heal with.
Rinse and repeat, and don't be impatient when the second Elise shows up. Rushing in and whacking at both of them is the easiest way to suddenly receive large amounts of damage when they spam their faster spells. Make sure you're at about 150 HP before the last Shadow Elise dies, since you won't have a chance to heal before the next battle.
Form 2 -- The Archdevil (The Showdown)
- White Gauntlet
- Same three magical charms
I admit, this battle is absolutely insane. The difficulty spikes up ridiculously at this point in the game against an enemy whose spammed attacks deal far more damage and have far more range than anything else encountered before. That being said, wearing three magical charms goes a long way towards making this battle seem less insurmountable and more simply challenging. 150 magical defense reduces the damage of his water rays and fire spinning spells to around -5 HP; casting super armor makes these attacks negligible.
The general strategy is to rush in, deal two or three strikes to one of his hands, and then run back because he's most likely about to either shoot thunder from his hands or spin flames from his core(perhaps even both). Wait for the attacks to subside and then repeat until one of the hands is dead. While you're doing this, keep an eye on his hands to make sure they don't start glowing; if both hands start glowing and come together, start dodging to the left or right to get away from his hands as quickly as possible, because he's about to shoot a massive fire ray that can deal up to 110 damage even with all your magic protection. If he sends bombs out to follow you, run away from the bombs until they all safely explode(lure them towards the hands if possible for extra damage, but it's often not worth it) and then go back to attacking the hands.
Once one of the hands goes down, many magical gems fly out. If you're at around 150 health or below, seek out three blue gems and use them to heal. Otherwise, look for four-of-a-kind and cast the spirit. Go up to the core and switch to the elemental gem that is super effective against the spirit type you just sent(fire against water, earth against wind, and vice-versa). Wallop on the core until it becomes invulnerable again, and then run away. Rinse and repeat everything. You should take out about a quarter of his health each time you stun him.
Once he's half dead he turns red and his attacks become faster and more deadly; however, your magical charms still reduce the damage from the fire or water to 10 HP off. The process is still the same.
When you're going to kill him, heal to at least 100 health to make sure that you survive the next form.
Form #3 -- The Archdevil again (The Last Battle)
After the chaos that Form #2 brings, Form #3 is a nice return to a boss with a very predictable and limited array of moves. Furthermore, the fireballs he shoots (oddly inflicting physical as opposed to magical damage, requiring a switch from charms to shields) are practically harmless with even only a Common Shield on.
He has four moves:
- large slow fireballs: go from side to side to avoid these, dodge inbetween the fireballs if you have to
- large spread fireballs: stick to one of the sides or the very center and these are easy to dodge
- alternating left and right fireballs: go left, then right, then left, then right
- laser beams: simply stand where the lasers don't touch. Attack him with a jump during this move since a grounded attack might accidentally move you into laser contact.
Simply dodge these moves and keep on firing fairy dust bullets. Eventually he's dead!
Congrats, you just won Chantelise! Enjoy the ending.