Quale's stats are low, other than his/her HP, which is the highest in the game tied with the friendly Yan's HP. Quale casts spells that inflict status effects, such as Poison, Darkness, Confuse, Silence and Mini. Quale absorbs Water damage and uses Water spells that hit the whole party. Quale's physical attack is called Rolling Attack, and it is quite powerful.
Immunity abilities like Antibody, Bright Eyes, Clear Headed and Loudmouth can be equipped as a counter measure to Quale's status-inflicting attacks. One cannot protect against Mini, but Quina's Blue Magic, Angel's Snack, can be used to cure it easily.
If the party doesn't have enough abilities/ability stones to adequately protect against Quale's status attacks, one can equip Auto-Reflect to bounce the spells back, but this will also reflect Quale's Water spells, which s/he will absorb. For the same reason, if Vivi/Amarant are in the party, one should not equip them with the Return Magic ability.
It is possible to stop Quale from casting his/her status inflicting spells if one drains his MP with Quina's Magic Hammer ability. However, this causes Quale to continuously attack with his powerful Rolling Attack.