Which Abilities are Terrible for Competitive, but GREAT for Casual Play?

All Pokémon have abilities, and sometimes they become a lethal combination and soar to the top of the competitive scene! (Or so I hear...) However sometimes a Pokémon can be written off as having a "bad" ability, but they're just not designed for battling on the front lines and their purpose lies somewhere else! So let's see which abilities are the best for Casual play!