Initial Mode:
Cagnazzo attacks characters once  - (not useful)
Change into "Water Form"

While in "Water Form":
Display message == "Water is gathering" or whatever
Change weakness to Lightning (while under this state)
Cast Wave on enemy (1/25 of Caster's HP)
Cast Haste on self
Repeat "Water Form" script
If hit by a Lightning magic attack while under "Water Mode", goto Initial Mode
Also Display message == "Lightning neutralizes water" or whatever

At any time, current HP < 700 (not sure if that's an exact number) Always Change To "Shell Mode":
Display message = "Monster hides in shell" or whatever
Set Defense to 3 (while under this state) - Edit: Yes, that's really 3, which is not a significant increase.
Cast Remedy/Heal/Restore (different names for the same spell) - (heals 1/10 of Caster's Max HP)
Repeat script while current HP < 700
Else Change Into "Water Form"

This defense change never occurs... it seems like the FF4A Euro version has this fixed. It may be worth looking into further.

Battle script (0x9D):
( $2 $0 $0 $2 )
    Target Enemies in Current Group
    Cast Remedy ($84)
    (End of Turn)
    Defense $7A
    $F3 to $F8 -  $81
    Do Nothing
( $2 $0 $0 $1 )
    Start Attack Chain
    $F3 to $F8 -  $81
    Do Nothing
    Chain with
    Battle Message $46
    Do Nothing
    Chain with
    Graphics $13
    Do Nothing
    Chain with
    Elemental Weakness $4
    Do Nothing
    End Attack Chain
    (End of Turn)
    Cast Wave ($9D)
    (End of Turn)
    Target Enemies in Current Group
    Cast Fast
Always
    Fight
    $F3 to $F8 -  $81
    
    
Counter script (0x9E):
If Self has less than 700 HP
If Receives a Damage Counter
    Start Attack Chain
    $F3 to $F8 -  $82
    Do Nothing
    Chain with
    $F3 to $F8 -  $80
    Do Nothing
    Chain with
    Graphics $14
    Do Nothing
    Chain with
    Elemental Weakness $2
    Do Nothing
    Chain with
    Battle Message $47
    Do Nothing
    End Attack Chain
( $2 $0 $1 $1 )
If Casted on by Character with Lightning
    Start Attack Chain
    $F3 to $F8 -  $80
    Do Nothing
    Chain with
    $F3 to $F8 -  $80
    Do Nothing
    Chain with
    Graphics $12
    Do Nothing
    Chain with
    Elemental Weakness $2
    Do Nothing
    Chain with
    Battle Message $74
    Do Nothing
    End Attack Chain