Iris doesn't join the battle
Give Maxim the Cold rapier, found on Treasure Sword Shrine B1. Normal attacks become ice-element, and the IP skill Glacial blast deals 3x normal damage.
The Rod Selan starts with gives normal attacks the anti-hard element
Both party members can learn the ice spell Gale (500G) at the spell shop in Tanbel or Clamento
Plasma blaster is a thunder attack on the whole party (power 180), Idura thunder is Bolt on the whole party, and normal attacks are thunder-element too
The Groupie it summons is weak to thunder, and its normal attacks have a 10% chance of sleep. Party members wearing the Mystery ring, found on North Lighthouse 1F, can't fall asleep. If one does, wake them with Awake.
Freeze magic, instant death, paralysis, and confusion have no effect, but sleep and poison do. Selan knows Drowsy from the start, so she can put it to sleep.