Rotdhizons!! Everytime. They have 12AP, have tonnes of Hp, completly Immune to Acid and Poison, Inflict Acid, Inflict Poison upon death, do a fair amount of damage, and sometimes get a quick action second swing. I love those things.
However, they suck against magic damage. Wingbolts and Kyshakks kill them. Gazers however arn't a problem.